Method and system for optimizing scanning of coherent lidar

ABSTRACT

An apparatus include a motor, a first scanner, and a second scanner. The first scanner is coupled to the motor, and the motor is configured to rotate the first scanner at a first angular velocity about a rotation axis to deflect a first beam incident in a third plane on the first scanner into a first plane different from the third plane. The second scanner is coupled to the motor, and the motor is configured to rotate the second scanner at a second angular velocity different from the first angular velocity about the rotation axis to deflect a second beam incident in the third plane on the second scanner into a second plane different from the third plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Application No. 62/739,915, filed Oct. 2, 2018, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

Optical detection of range using lasers, often referenced by a mnemonic,LIDAR, for light detection and ranging, also sometimes called laserRADAR, is used for a variety of applications, from altimetry, toimaging, to collision avoidance. LIDAR provides finer scale rangeresolution with smaller beam sizes than conventional microwave rangingsystems, such as radio-wave detection and ranging (RADAR).

SUMMARY

At least one aspect relates to an apparatus. The apparatus includes amotor, a first scanner, and a second scanner. The first scanner iscoupled to the motor, and the motor is configured to rotate the firstscanner at a first angular velocity about a rotation axis to deflect afirst beam incident in a third plane on the first scanner into a firstplane different from the third plane. The second scanner is coupled tothe motor, and the motor is configured to rotate the second scanner at asecond angular velocity different from the first angular velocity aboutthe rotation axis to deflect a second beam incident in the third planeon the second scanner into a second plane different from the thirdplane.

At least one aspect relates to a system. The system includes a lasersource, at least one waveguide, at least one collimator, a motor, afirst scanner, and a second scanner. The at least one waveguide isconfigured to receive a third beam from the laser source and emit thethird beam at a tip of the at least one waveguide. The at least onecollimator is configured to collimate the third beam from eachrespective at least one waveguide into a third plane. The first scanneris coupled to the motor, and the motor is configured to rotate the firstscanner to deflect a first beam corresponding to the third beam into afirst plane different from the third plane. The second scanner iscoupled to the motor, and the motor is configured to rotate the secondscanner to deflect a second beam corresponding to the third beam into asecond plane different from the third plane.

Those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Any ofthe features described herein may be used with any other features, andany subset of such features can be used in combination according tovarious embodiments. Other aspects, inventive features, and advantagesof the devices and/or processes described herein, as defined solely bythe claims, will become apparent in the detailed description set forthherein and taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements and in which:

FIG. 1A is a schematic graph that illustrates the example transmittedsignal of a series of binary digits along with returned optical signalsfor measurement of range, according to an embodiment;

FIG. 1B is a schematic graph that illustrates an example spectrum of thereference signal and an example spectrum of a Doppler shifted returnsignal, according to an embodiment;

FIG. 1C is a schematic graph that illustrates an example cross-spectrumof phase components of a Doppler shifted return signal, according to anembodiment;

FIG. 1D is a set of graphs that illustrates an example optical chirpmeasurement of range, according to an embodiment;

FIG. 1E is a graph using a symmetric LO signal, and shows the returnsignal in this frequency time plot as a dashed line when there is noDoppler shift, according to an embodiment;

FIG. 1F is a graph similar to FIG. 1E, using a symmetric LO signal, andshows the return signal in this frequency time plot as a dashed linewhen there is a non zero Doppler shift, according to an embodiment;

FIG. 2A is a block diagram that illustrates example components of a highresolution (hi res) LIDAR system, according to an embodiment;

FIG. 2B is a block diagram that illustrates a saw tooth scan pattern fora hi-res Doppler system, used in some embodiments;

FIG. 2C is an image that illustrates an example speed point cloudproduced by a hi-res Doppler LIDAR system, according to an embodiment;

FIG. 2D is a block diagram that illustrates example components of a highresolution (hi res) LIDAR system, according to an embodiment;

FIG. 2E is a block diagram that illustrates a side view of examplecomponents of a high resolution (hi res) LIDAR system, according to anembodiment;

FIG. 2F is a block diagram that illustrates a top view of the examplecomponents of the high resolution (hi res) LIDAR system of FIG. 2E,according to an embodiment;

FIG. 2G is a block diagram that illustrates a side view of examplecomponents of a high resolution (hi res) LIDAR system, according to anembodiment;

FIG. 2H is a block diagram that illustrates a top view of the examplecomponents of the high resolution (hi res) LIDAR system of FIG. 2G,according to an embodiment;

FIG. 2I is a schematic diagram that illustrates an exploded view of thescanning optics of the system of FIG. 2E, according to an embodiment;

FIG. 2J is a schematic diagram that illustrates a side view of multiplebeams scanned in multiple scan regions of the system of FIG. 2E,according to an embodiment;

FIG. 2K is a schematic diagram that illustrates a cross sectional viewof the multiple scan regions of FIG. 2J taken along the line 2K-2K;

FIG. 3A is a block diagram that illustrates an example system thatincludes at least one hi-res LIDAR system mounted on a vehicle,according to an embodiment;

FIG. 3B is a block diagram that illustrates an example system thatincludes at least one hi-res LIDAR system mounted on a vehicle,according to an embodiment;

FIG. 4A is a graph that illustrates an example signal-to-noise ratio(SNR) versus target range for the transmitted signal in the system ofFIG. 2D without scanning, according to an embodiment;

FIG. 4B is a graph that illustrates an example of a curve indicating a1/r-squared loss that drives the shape of the SNR curve of FIG. 4A inthe far field, according to an embodiment;

FIG. 4C is a graph that illustrates an example of collimated beamdiameter versus range for the transmitted signal in the system of FIG.2D without scanning, according to an embodiment;

FIG. 4D is a graph that illustrates an example of SNR associated withcollection efficiency versus range for the transmitted signal in thesystem of FIG. 2D without scanning, according to an embodiment;

FIG. 4E is an image that illustrates an example of beam walkoff forvarious target ranges and scan speeds in the system of FIG. 2D,according to an embodiment;

FIG. 4F is a graph that illustrates an example of coupling efficiencyversus target range for various scan rates in the system of FIG. 2D,according to an embodiment;

FIG. 4G is a graph that illustrates an example of SNR versus targetrange for various scan rates in the system of FIG. 2D, according to anembodiment;

FIG. 4H is a graph that illustrates an example of SNR versus targetrange for various integration times in the system of FIG. 2D, accordingto an embodiment;

FIG. 4I is a graph that illustrates an example of a measurement rateversus target range in the system of FIG. 2D, according to anembodiment;

FIG. 5 is a flow chart that illustrates an example method for optimizinga scan pattern of a LIDAR system on an autonomous vehicle, according toan embodiment;

FIG. 6 is a flow chart that illustrates an example method for operatinga LIDAR system on an autonomous vehicle, according to an embodiment;

FIG. 7 is a block diagram that illustrates a computer system upon whichan embodiment of the invention may be implemented; and

FIG. 8 illustrates a chip set upon which an embodiment of the inventionmay be implemented.

DETAILED DESCRIPTION

A method and apparatus and system and computer-readable medium aredescribed for scanning of LIDAR to support operation of a vehicle. Someembodiments are described below in the context of a single front mountedhi-res Doppler LIDAR system on a personal automobile; but, embodimentsare not limited to this context. In other embodiments, one or multiplesystems of the same type or other high resolution LIDAR, with or withoutDoppler components, with overlapping or non-overlapping fields of viewor one or more such systems mounted on smaller or larger land, sea orair vehicles, piloted or autonomous, are employed.

The sampling and processing that provides range accuracy and targetspeed accuracy involve integration of one or more laser signals ofvarious durations, in a time interval called integration time. To covera scene in a timely way involves repeating a measurement of sufficientaccuracy (involving one or more signals often over one to tens ofmicroseconds) often enough to sample a variety of angles (often on theorder of thousands) around the autonomous vehicle to understand theenvironment around the vehicle before the vehicle advances too far intothe space ahead of the vehicle (a distance on the order of one to tensof meters, often covered in a particular time on the order of one to afew seconds). The number of different angles that can be covered in theparticular time (often called the cycle or sampling time) depends on thesampling rate. To improve detection of an environment around a vehicle,one or more scanners may be controlled to rotate based on parametersincluding at least one of integration time for range, speed accuracy,sampling rate, or pattern of sampling different angles. In particular, atradeoff can be made between integration time for range and speedaccuracy, sampling rate, and pattern of sampling different angles, withone or more LIDAR beams, to effectively determine the environment in thevicinity of an autonomous vehicle as the vehicle moves through thatenvironment. Optical detection of range can be accomplished with severaldifferent techniques, including direct ranging based on round triptravel time of an optical pulse to an object, and chirped detectionbased on a frequency difference between a transmitted chirped opticalsignal and a returned signal scattered from an object, and phase-encodeddetection based on a sequence of single frequency phase changes that aredistinguishable from natural signals.

A method can include generating, with a LIDAR system including a lasersource and a waveguide, a beam emitted from a tip of the waveguide. Themethod also includes shaping, with a collimator, the beam incident in athird plane on one of a first polygon scanner and a second polygonscanner of the LIDAR system. The method also includes adjusting, withthe first polygon scanner, a direction of the beam in a first planedifferent from the third plane from a first angle to a second anglewithin the first plane based on rotation of the first polygon scannerabout a rotation axis with a first angular velocity. The method alsoincludes receiving, at the tip of the waveguide, a plurality of firstreturn beams based on the adjusting of the beam in the first plane toencompass a first scan region of a target positioned at a first range.The method also includes adjusting, with the second polygon scanner, adirection of the beam in a second plane different from the third planefrom a first angle to a second angle within the second plane based onrotation of the second polygon scanner about the rotation axis with asecond angular velocity different than the first angular velocity. Themethod also includes receiving, at the tip of the waveguide, a pluralityof second return beams based on the adjusting of the beam in the secondplane to encompass a second scan region of a target positioned at asecond range different from the first range.

A method can include receiving, on a processor, first data thatindicates first signal-to-noise ratio (SNR) values of a signal reflectedby a target and detected by the LIDAR system based on values of a rangeof the target, where the first SNR values are for a respective value ofa scan rate of the LIDAR system. The first data also indicates secondsignal-to-noise ratio (SNR) values of the signal based on values of therange of the target, where the second SNR values are for a respectivevalue of an integration time of the LIDAR system. The first data alsoindicates a first angle and a second angle that defines an angle rangeof the scan pattern. The method also includes receiving, on theprocessor, second data that indicates a first maximum design range ofthe target at each angle in the angle range for a first scan region anda second maximum design range of the target at each angle in the anglefor a second scan region different than the first scan region. Themethod also includes for each angle in the angle range of the first scanregion, determining, on the processor, a first maximum scan rate of theLIDAR system based on a maximum value among those scan rates where thefirst SNR value based on the first maximum design range is greater thana minimum SNR threshold. The method also includes for each angle in theangle range of the second scan region, determining, on the processor, asecond maximum scan rate of the LIDAR system based on a maximum valueamong those scan rates where the first SNR value based on the secondmaximum design range is greater than a minimum SNR threshold. The methodalso includes for each angle in the angle range of the first scanregion, determining, on the processor, a first minimum integration timeof the LIDAR system based on a minimum value among those integrationtimes where the second SNR value based on the first maximum design rangeis greater than the minimum SNR threshold. The method also includes foreach angle in the angle range of the second scan region, determining, onthe processor, a second minimum integration time of the LIDAR systembased on a minimum value among those integration times where the secondSNR value based on the second maximum design range is greater than theminimum SNR threshold. The method also includes defining, with theprocessor, the scan pattern for the first scan region of the LIDARsystem based on the first maximum scan rate and the first minimumintegration time at each angle in the angle range of the first scanregion. The method also includes defining, with the processor, the scanpattern for the second scan region of the LIDAR system based on thesecond maximum scan rate and the second minimum integration time at eachangle in the angle range of the first scan region. The method alsoincludes operating the LIDAR system according to the scan pattern forthe first scan region and the second scan region.

1. Phase-Encoded Detection Overview

Using an optical phase-encoded signal for measurement of range, thetransmitted signal is in phase with a carrier (phase=0) for part of thetransmitted signal and then changes by one or more phases changesrepresented by the symbol Δϕ (so phase=Δϕ) for short time intervals,switching back and forth between the two or more phase values repeatedlyover the transmitted signal. The shortest interval of constant phase isa parameter of the encoding called pulse duration τ and is typically theduration of several periods of the lowest frequency in the band. Thereciprocal, 1/τ, is baud rate, where each baud indicates a symbol. Thenumber N of such constant phase pulses during the time of thetransmitted signal is the number N of symbols and represents the lengthof the encoding. In binary encoding, there are two phase values and thephase of the shortest interval can be considered a 0 for one value and a1 for the other, thus the symbol is one bit, and the baud rate is alsocalled the bit rate. In multiphase encoding, there are multiple phasevalues. For example, 4 phase values such as Δϕ* {0, 1, 2 and 3}, which,for Δϕ=π/2 (90 degrees), equals {0, π/2, π and 3π/2}, respectively; and,thus 4 phase values can represent 0, 1, 2, 3, respectively. In thisexample, each symbol is two bits and the bit rate is twice the baudrate.

Phase-shift keying (PSK) refers to a digital modulation scheme thatconveys data by changing (modulating) the phase of a reference signal(the carrier wave). The modulation is impressed by varying the sine andcosine inputs at a precise time. At radio frequencies (RF), PSK iswidely used for wireless local area networks (LANs), RF identification(RFID) and Bluetooth communication. Alternatively, instead of operatingwith respect to a constant reference wave, the transmission can operatewith respect to itself. Changes in phase of a single transmittedwaveform can be considered the symbol. In this system, the demodulatordetermines the changes in the phase of the received signal rather thanthe phase (relative to a reference wave) itself. Since this schemedepends on the difference between successive phases, it is termeddifferential phase-shift keying (DPSK). DPSK can be significantlysimpler to implement in communications applications than ordinary PSK,since there is no need for the demodulator to have a copy of thereference signal to determine the exact phase of the received signal(thus, it is a non-coherent scheme).

To achieve acceptable range accuracy and detection sensitivity, directlong range LIDAR systems may use short pulse lasers with low pulserepetition rate and extremely high pulse peak power. The high pulsepower can lead to rapid degradation of optical components. Chirped andphase-encoded LIDAR systems may use long optical pulses with relativelylow peak optical power. In this configuration, the range accuracy canincrease with the chirp bandwidth or length and bandwidth of the phasecodes rather than the pulse duration, and therefore excellent rangeaccuracy can still be obtained.

Useful optical bandwidths have been achieved using wideband radiofrequency (RF) electrical signals to modulate an optical carrier. Withrespect to LIDAR, using the same modulated optical carrier as areference signal that is combined with the returned signal at an opticaldetector can produce in the resulting electrical signal a relatively lowbeat frequency in the RF band that is proportional to the difference infrequencies or phases between the references and returned opticalsignals. This kind of beat frequency detection of frequency differencesat a detector is called heterodyne detection, which can enable using RFcomponents of ready and inexpensive availability.

High resolution range-Doppler LIDAR systems can use an arrangement ofoptical components and coherent processing to detect Doppler shifts inreturned signals to provide improved range and relative signed speed ona vector between the LIDAR system and each external object.

In some instances, these improvements provide range, with or withouttarget speed, in a pencil thin laser beam of proper frequency or phasecontent. When such beams are swept over a scene, information about thelocation and speed of surrounding objects can be obtained. Thisinformation can be used in control systems for autonomous vehicles, suchas self driving, or driver assisted, automobiles.

For optical ranging applications, since the transmitter and receiver arein the same device, coherent PSK can be used. The carrier frequency isan optical frequency f_(C) and a RF f₀ is modulated onto the opticalcarrier. The number N and duration r of symbols are selected to achievethe desired range accuracy and resolution. The pattern of symbols isselected to be distinguishable from other sources of coded signals andnoise. Thus a strong correlation between the transmitted and returnedsignal can be a strong indication of a reflected or backscatteredsignal. The transmitted signal is made up of one or more blocks ofsymbols, where each block is sufficiently long to provide strongcorrelation with a reflected or backscattered return even in thepresence of noise. The transmitted signal can be made up of M blocks ofN symbols per block, where M and N are non-negative integers.

FIG. 1A is a schematic graph 120 that illustrates the exampletransmitted signal as a series of binary digits along with returnedoptical signals for measurement of range, according to an embodiment.The horizontal axis 122 indicates time in arbitrary units after a starttime at zero. The vertical axis 124 a indicates amplitude of an opticaltransmitted signal at frequency f_(C)+f₀ in arbitrary units relative tozero. The vertical axis 124 b indicates amplitude of an optical returnedsignal at frequency f_(C)+f₀ in arbitrary units relative to zero, and isoffset from axis 124 a to separate traces. Trace 125 represents atransmitted signal of M*N binary symbols, with phase changes as shown inFIG. 1A to produce a code starting with 00011010 and continuing asindicated by ellipsis. Trace 126 represents an idealized (noiseless)return signal that is scattered from an object that is not moving (andthus the return is not Doppler shifted). The amplitude is reduced, butthe code 00011010 is recognizable. Trace 127 represents an idealized(noiseless) return signal that is scattered from an object that ismoving and is therefore Doppler shifted. The return is not at the properoptical frequency f_(C)+f₀ and is not well detected in the expectedfrequency band, so the amplitude is diminished.

The observed frequency f′ of the return differs from the correctfrequency f=f_(C)+f₀ of the return by the Doppler effect given byEquation 1.

$\begin{matrix}{f^{\prime} = {\frac{\left( {c + v_{o}} \right)}{\left( {c + v_{s}} \right)}f}} & (1)\end{matrix}$

Where c is the speed of light in the medium, v_(o) is the velocity ofthe observer and v_(s) is the velocity of the source along the vectorconnecting source to receiver. Note that the two frequencies are thesame if the observer and source are moving at the same speed in the samedirection on the vector between the two. The difference between the twofrequencies, Δf=f′−f , is the Doppler shift, Δf_(D), which causesproblems for the range measurement, and is given by Equation 2.

$\begin{matrix}{{\Delta \; f_{D}} = {\left\lbrack {\frac{\left( {c + v_{o}} \right)}{\left( {c + v_{s}} \right)} - 1} \right\rbrack f}} & (2)\end{matrix}$

Note that the magnitude of the error increases with the frequency f ofthe signal. Note also that for a stationary LIDAR system (v_(o)=0), foran object moving at 10 meters a second (v_(s)=10), and visible light offrequency about 500 THz, then the size of the error is on the order of16 megahertz (MHz, 1 MHz=10⁶ hertz, Hz, 1 Hz=1 cycle per second). Invarious embodiments described below, the Doppler shift error is detectedand used to process the data for the calculation of range.

In phase coded ranging, the arrival of the phase coded reflection can bedetected in the return by cross correlating the transmitted signal orother reference signal with the returned signal, which can beimplemented by cross correlating the code for a RF signal with anelectrical signal from an optical detector using heterodyne detectionand thus down-mixing back to the RF band. Cross correlation for any onelag can be computed by convolving the two traces, such as by multiplyingcorresponding values in the two traces and summing over all points inthe trace, and then repeating for each time lag. The cross correlationcan be accomplished by a multiplication of the Fourier transforms ofeach of the two traces followed by an inverse Fourier transform. Forwardand inverse Fast Fourier transforms (FFTs) can be efficientlyimplemented in hardware and software.

Note that the cross correlation computation may be done with analog ordigital electrical signals after the amplitude and phase of the returnis detected at an optical detector. To move the signal at the opticaldetector to a RF frequency range that can be digitized easily, theoptical return signal is optically mixed with the reference signalbefore impinging on the detector. A copy of the phase-encodedtransmitted optical signal can be used as the reference signal, but itis also possible, and often preferable, to use the continuous wavecarrier frequency optical signal output by the laser as the referencesignal and capture both the amplitude and phase of the electrical signaloutput by the detector.

For an idealized (noiseless) return signal that is reflected from anobject that is not moving (and thus the return is not Doppler shifted),a peak occurs at a time Δt after the start of the transmitted signal.This indicates that the returned signal includes a version of thetransmitted phase code beginning at the time Δt. The range R to thereflecting (or backscattering) object is computed from the two waytravel time delay based on the speed of light c in the medium, as givenby Equation 3.

R=c*Δt/2   (3)

For an idealized (noiseless) return signal that is scattered from anobject that is moving (and thus the return is Doppler shifted), thereturn signal does not include the phase encoding in the properfrequency bin, the correlation stays low for all time lags, and a peakis not as readily detected, and is often undetectable in the presence ofnoise. Thus Δt is not as readily determined and range R is not asreadily produced.

The Doppler shift can be determined in the electrical processing of thereturned signal, and can be used to correct the cross correlationcalculation. Thus a peak can be more readily found and range can be morereadily determined. FIG. 1B is a schematic graph 140 that illustrates anexample spectrum of the transmitted signal and an example spectrum of aDoppler shifted complex return signal, according to an embodiment. Thehorizontal axis 142 indicates RF frequency offset from an opticalcarrier f_(C) in arbitrary units. The vertical axis 144 a indicatesamplitude of a particular narrow frequency bin, also called spectraldensity, in arbitrary units relative to zero. The vertical axis 144 bindicates spectral density in arbitrary units relative to zero, and isoffset from axis 144 a to separate traces. Trace 145 represents atransmitted signal; and, a peak occurs at the proper RF f₀. Trace 146represents an idealized (noiseless) complex return signal that isbackscattered from an object that is moving toward the LIDAR system andis therefore Doppler shifted to a higher frequency (called blueshifted). The return does not have a peak at the proper RF f₀; but,instead, is blue shifted by Δf_(D) to a shifted frequency f_(S). Inpractice, a complex return representing both in-phase and quadrature(I/Q) components of the return is used to determine the peak at +Δf_(D),thus the direction of the Doppler shift, and the direction of motion ofthe target on the vector between the sensor and the object, can bedetected from a single return.

In some Doppler compensation embodiments, rather than finding Δf_(D) bytaking the spectrum of both transmitted and returned signals andsearching for peaks in each, then subtracting the frequencies ofcorresponding peaks, as illustrated in FIG. 1B, it can be more efficientto take the cross spectrum of the in-phase and quadrature component ofthe down-mixed returned signal in the RF band. FIG. 1C is a schematicgraph 150 that illustrates an example cross-spectrum, according to anembodiment. The horizontal axis 152 indicates frequency shift inarbitrary units relative to the reference spectrum; and, the verticalaxis 154 indicates amplitude of the cross spectrum in arbitrary unitsrelative to zero. Trace 155 represents a cross spectrum with anidealized (noiseless) return signal generated by one object movingtoward the LIDAR system (blue shift of Δf_(D1)=Δf_(D) in FIG. 1B) and asecond object moving away from the LIDAR system (red shift of Δf_(D2)).A peak 156 a occurs when one of the components is blue shifted Δf_(D1);and, another peak 156 b occurs when one of the components is red shiftedΔf_(D2). Thus the Doppler shifts are determined. These shifts can beused to determine a signed velocity of approach of objects in thevicinity of the LIDAR, such as for collision avoidance applications.However, if I/Q processing is not done, peaks may appear at both+/−Δf_(D1) and both +/−Δf_(D2), so there may be ambiguity on the sign ofthe Doppler shift and thus the direction of movement.

The Doppler shift(s) detected in the cross spectrum can be used tocorrect the cross correlation so that the peak 135 is apparent in theDoppler compensated Doppler shifted return at lag Δt, and range R can bedetermined. In some embodiments, simultaneous I/Q processing can beperformed. In some embodiments, serial I/Q processing can be used todetermine the sign of the Doppler return. In some embodiments, errorsdue to Doppler shifting can be tolerated or ignored; and, no Dopplercorrection is applied to the range measurements.

2. Chirped Detection Overview

FIG. 1D is a set of graphs that illustrates an example optical chirpmeasurement of range, according to an embodiment. The horizontal axis102 is the same for all four graphs and indicates time in arbitraryunits, on the order of milliseconds (ms, 1 ms=10⁻³ seconds). Graph 100indicates the power of a beam of light used as a transmitted opticalsignal. The vertical axis 104 in graph 100 indicates power of thetransmitted signal in arbitrary units. Trace 106 indicates that thepower is on for a limited pulse duration, τ starting at time 0. Graph110 indicates the frequency of the transmitted signal. The vertical axis114 indicates the frequency transmitted in arbitrary units. The trace116 indicates that the frequency of the pulse increases from f₁ to f₂over the duration τ of the pulse, and thus has a bandwidth B=f₂−f₁. Thefrequency rate of change is (f₂−f₁)/τ.

The returned signal is depicted in graph 160 which has a horizontal axis102 that indicates time and a vertical axis 114 that indicates frequencyas in graph 110. The chirp (e.g., trace 116) of graph 110 is alsoplotted as a dotted line on graph 160. A first returned signal is givenby trace 166 a, which can represent the transmitted reference signaldiminished in intensity (not shown) and delayed by Δt. When the returnedsignal is received from an external object after covering a distance of2R, where R is the range to the target, the returned signal start at thedelayed time Δt can be given by 2R/c, where c is the speed of light inthe medium (approximately 3×10⁸ meters per second, m/s), relatedaccording to Equation 3, described above. Over this time, the frequencyhas changed by an amount that depends on the range, called f_(R), andgiven by the frequency rate of change multiplied by the delay time. Thisis given by Equation 4a.

f _(R)=(f ₂ −f ₁)/τ*2R/c=2BR/cτ  (4a)

The value of f_(R) can be measured by the frequency difference betweenthe transmitted signal 116 and returned signal 166 a in a time domainmixing operation referred to as de-chirping. So the range R is given byEquation 4b.

R=f _(R) c τ/2B   (4b)

If the returned signal arrives after the pulse is completelytransmitted, that is, if 2R/c is greater than τ, then Equations 4a and4b are not valid. In this case, the reference signal can be delayed aknown or fixed amount to ensure the returned signal overlaps thereference signal. The fixed or known delay time of the reference signalcan be multiplied by the speed of light, c, to give an additional rangethat is added to range computed from Equation 4b. While the absoluterange may be off due to uncertainty of the speed of light in the medium,this is a near-constant error and the relative ranges based on thefrequency difference are still very precise.

In some circumstances, a spot illuminated (pencil beam cross section) bythe transmitted light beam encounters two or more different scatterersat different ranges, such as a front and a back of a semitransparentobject, or the closer and farther portions of an object at varyingdistances from the LIDAR, or two separate objects within the illuminatedspot. In such circumstances, a second diminished intensity anddifferently delayed signal will also be received, indicated on graph 160by trace 166 b. This will have a different measured value of f_(R) thatgives a different range using Equation 4b. In some circumstances,multiple additional returned signals are received.

Graph 170 depicts the difference frequency f_(R) between a firstreturned signal 166 a and the reference chirp 116. The horizontal axis102 indicates time as in all the other aligned graphs in FIG. 1D, andthe vertical axis 164 indicates frequency difference on a much expandedscale. Trace 176 depicts the constant frequency f_(R) measured inresponse to the transmitted chirp, which indicates a particular range asgiven by Equation 4b. The second returned signal 166 b, if present,would give rise to a different, larger value of f_(R) (not shown) duringde-chirping; and, as a consequence yield a larger range using Equation4b.

De-chirping can be performed by directing both the reference opticalsignal and the returned optical signal to the same optical detector. Theelectrical output of the detector may be dominated by a beat frequencythat is equal to, or otherwise depends on, the difference in thefrequencies of the two signals converging on the detector. A Fouriertransform of this electrical output signal will yield a peak at the beatfrequency. This beat frequency is in the radio frequency (RF) range ofMegahertz (MHz, 1 MHz=10⁶ Hertz=10⁶ cycles per second) rather than inthe optical frequency range of Terahertz (THz, 1 THz=10¹² Hertz). Suchsignals can be processed by RF components, such as a Fast FourierTransform (FFT) algorithm running on a microprocessor or a speciallybuilt FFT or other digital signal processing (DSP) integrated circuit.The return signal can be mixed with a continuous wave (CW) tone actingas the local oscillator (versus a chirp as the local oscillator). Thisleads to the detected signal which itself is a chirp (or whateverwaveform was transmitted). In this case the detected signal can undergomatched filtering in the digital domain, though the digitizer bandwidthrequirement may generally be higher. The positive aspects of coherentdetection are otherwise retained.

In some embodiments, the LIDAR system is changed to produce simultaneousup and down chirps. This approach can eliminate variability introducedby object speed differences, or LIDAR position changes relative to theobject which actually does change the range, or transient scatterers inthe beam, among others, or some combination. The approach may guaranteethat the Doppler shifts and ranges measured on the up and down chirpsare indeed identical and can be most usefully combined. The Dopplerscheme may guarantee parallel capture of asymmetrically shifted returnpairs in frequency space for a high probability of correct compensation.

FIG. 1E is a graph using a symmetric LO signal, and shows the returnsignal in this frequency time plot as a dashed line when there is noDoppler shift, according to an embodiment. The horizontal axis indicatestime in example units of 10⁻⁵ seconds (tens of microseconds). Thevertical axis indicates frequency of the optical transmitted signalrelative to the carrier frequency f_(c) or reference signal in exampleunits of GigaHertz (10⁹ Hertz). During a pulse duration, a light beamcomprising two optical frequencies at any time is generated. Onefrequency increases from f₁ to f₂ (e.g., 1 to 2 GHz above the opticalcarrier) while the other frequency simultaneous decreases from f₄ to f₃(e.g., 1 to 2 GHz below the optical carrier) The two frequency bandse.g., band 1 from f₁ to f₂, and band 2 from f₃ to f₄) do not overlap sothat both transmitted and return signals can be optically separated by ahigh pass or a low pass filter, or some combination, with pass bandsstarting at pass frequency f_(p). For example f₁<f₂<f_(p)<f₃<f₄. Asillustrated, the higher frequencies can provide the up chirp and thelower frequencies can provide the down chirp. In some embodiments, thehigher frequencies produce the down chirp and the lower frequenciesproduce the up chirp.

In some embodiments, two different laser sources are used to produce thetwo different optical frequencies in each beam at each time. In someembodiments, a single optical carrier is modulated by a single RF chirpto produce symmetrical sidebands that serve as the simultaneous up anddown chirps. In some embodiments, a double sideband Mach-Zehnderintensity modulator is used that, in general, may not leave much energyin the carrier frequency; instead, almost all of the energy goes intothe sidebands.

As a result of sideband symmetry, the bandwidth of the two opticalchirps can be the same if the same order sideband is used. In someembodiments, other sidebands are used, e.g., two second order sidebandare used, or a first order sideband and a non-overlapping secondsideband is used, or some other combination.

When selecting the transmit (TX) and local oscillator (LO) chirpwaveforms, it can be advantageous to ensure that the frequency shiftedbands of the system take maximum advantage of available digitizerbandwidth. In general this can be accomplished by shifting either the upchirp or the down chirp to have a range frequency beat close to zero.

FIG. 1F is a graph similar to FIG. 1E, using a symmetric LO signal, andshows the return signal in this frequency time plot as a dashed linewhen there is a nonzero Doppler shift. In the case of a chirpedwaveform, the time separated I/Q processing (aka time domainmultiplexing) can be used to overcome hardware requirements of otherapproaches. In that case, an AOM can be used to break the range-Dopplerambiguity for real valued signals. In some embodiments, a scoring systemcan be used to pair the up and down chirp returns. In some embodiments,I/Q processing can be used to determine the sign of the Doppler chirp.

3. Optical Detection Hardware Overview

FIG. 2A is a block diagram that illustrates example components of a highresolution range LIDAR system 200, according to an embodiment. Opticalsignals are indicated by arrows. Electronic wired or wirelessconnections are indicated by segmented lines without arrowheads. A lasersource 212 emits a beam (e.g., carrier wave) 201 that is phase orfrequency modulated in modulator 282 a, before or after splitter 216, toproduce a phase coded or chirped optical signal 203 that has a durationD. A splitter 216 splits the modulated (or, as shown, the unmodulated)optical signal for use in a reference path 220. A target beam 205, alsocalled transmitted signal herein, with most of the energy of the beam201 can be produced. A modulated or unmodulated reference beam 207 a,which can have a much smaller amount of energy that is nonethelessenough to produce good mixing with the returned light 291 scattered froman object (not shown), can also be produced. As depicted in FIG. 2A, thereference beam 207 a is separately modulated in modulator 282 b. Thereference beam 207 a passes through reference path 220 and is directedto one or more detectors as reference beam 207 b. In some embodiments,the reference path 220 introduces a known delay sufficient for referencebeam 207 b to arrive at the detector array 230 with the scattered lightfrom an object outside the LIDAR within a spread of ranges of interest.In some embodiments, the reference beam 207 b is called the localoscillator (LO) signal, such as if the reference beam 207 b wereproduced locally from a separate oscillator. In various embodiments,from less to more flexible approaches, the reference can be caused toarrive with the scattered or reflected field by: 1) putting a mirror inthe scene to reflect a portion of the transmit beam back at the detectorarray so that path lengths are well matched; 2) using a fiber delay toclosely match the path length and broadcast the reference beam withoptics near the detector array, as suggested in FIG. 2A, with or withouta path length adjustment to compensate for the phase or frequencydifference observed or expected for a particular range; or, 3) using afrequency shifting device (acousto-optic modulator) or time delay of alocal oscillator waveform modulation (e.g., in modulator 282 b) toproduce a separate modulation to compensate for path length mismatch; orsome combination. In some embodiments, the object is close enough andthe transmitted duration long enough that the returns sufficientlyoverlap the reference signal without a delay.

The transmitted signal is then transmitted to illuminate an area ofinterest, such as through some scanning optics 218. The detector arraycan be a single paired or unpaired detector or a 1 dimensional (1D) or 2dimensional (2D) array of paired or unpaired detectors arranged in aplane roughly perpendicular to returned beams 291 from the object. Thereference beam 207 b and returned beam 291 can be combined in zero ormore optical mixers 284 to produce an optical signal of characteristicsto be properly detected. The frequency, phase or amplitude of theinterference pattern, or some combination, can be recorded byacquisition system 240 for each detector at multiple times during thesignal duration D. The number of temporal samples processed per signalduration or integration time can affect the down-range extent. Thenumber or integration time can be a practical consideration chosen basedon number of symbols per signal, signal repetition rate and availablecamera frame rate. The frame rate is the sampling bandwidth, oftencalled “digitizer frequency.” The only fundamental limitations of rangeextent are the coherence length of the laser and the length of the chirpor unique phase code before it repeats (for unambiguous ranging). Thisis enabled because any digital record of the returned heterodyne signalor bits could be compared or cross correlated with any portion oftransmitted bits from the prior transmission history.

The acquired data is made available to a processing system 250, such asa computer system described below with reference to FIG. 7, or a chipset described below with reference to FIG. 8. A scanner control module270 provides scanning signals to drive the scanning optics 218. Thescanner control module 270 can include instructions to perform one ormore steps of the method 500 related to the flowchart of FIG. 5 and/orthe method 600 related to the flowchart of FIG. 6. A signed Dopplercompensation module (not shown) in processing system 250 can determinethe sign and size of the Doppler shift and the corrected range basedthereon along with any other corrections. The processing system 250 alsocan include a modulation signal module (not shown) to send one or moreelectrical signals that drive modulators 282 a, 282 b and/or polygonscanners 244 a, 244 b and/or scanner 241. In some embodiments, theprocessing system also includes a vehicle control module 272 to controla vehicle on which the system 200, 200′, 200″ is installed.

Optical coupling to flood or focus on a target or focus past the pupilplane are not depicted. As used herein, an optical coupler is anycomponent that affects the propagation of light within spatialcoordinates to direct light from one component to another component,such as a vacuum, air, glass, crystal, mirror, lens, optical circulator,beam splitter, phase plate, polarizer, optical fiber, optical mixer,among others, alone or in some combination.

FIG. 2A also illustrates example components for a simultaneous up anddown chirp LIDAR system according to one embodiment. As depicted in FIG.2A, the modulator 282 a can be a frequency shifter added to the opticalpath of the transmitted beam 205. In some embodiments, the frequencyshifter is added to the optical path of the returned beam 291 or to thereference path 220. The frequency shifter can be added as modulator 282b on the local oscillator (LO, also called the reference path) side oron the transmit side (before the optical amplifier) as the device usedas the modulator (e.g., an acousto-optic modulator, AOM) has some lossassociated and it can be disadvantageous to put lossy components on thereceive side or after the optical amplifier. The optical shifter canshift the frequency of the transmitted signal (or return signal)relative to the frequency of the reference signal by a known amountΔf_(S), so that the beat frequencies of the up and down chirps occur indifferent frequency bands, which can be picked up, e.g., by the FFTcomponent in processing system 250, in the analysis of the electricalsignal output by the optical detector 230. For example, if the blueshift causing range effects is f_(B), then the beat frequency of the upchirp will be increased by the offset and occur at f_(B)+Δf_(S) and thebeat frequency of the down chirp will be decreased by the offset tof_(B)−Δf_(S). Thus, the up chirps will be in a higher frequency bandthan the down chirps, thereby separating them. If Δf_(S) is greater thanany expected Doppler effect, there will be no ambiguity in the rangesassociated with up chirps and down chirps. The measured beats can thenbe corrected with the correctly signed value of the known Δf_(S) to getthe proper up-chirp and down-chirp ranges. In some embodiments, the RFsignal coming out of the balanced detector is digitized directly withthe bands being separated via FFT. In some embodiments, the RF signalcoming out of the balanced detector is pre-processed with analog RFelectronics to separate a low-band (corresponding to one of the up chirpor down chip) which can be directly digitized and a high-band(corresponding to the opposite chirp) which can be electronicallydown-mixed to baseband and then digitized. Various such embodimentsoffer pathways that match the bands of the detected signals to availabledigitizer resources. In some embodiments, the modulator 282 a isexcluded (e.g. direct ranging).

FIG. 2B is a block diagram that illustrates a saw tooth scan pattern fora hi-res Doppler system. The scan sweeps through a range of azimuthangles (horizontally) and inclination angles (vertically above and belowa level direction at zero inclination). Various scan patterns can beused, including adaptive scanning. FIG. 2C is an image that illustratesan example speed point cloud produced by a hi-res Doppler LIDAR system.

FIG. 2D is a block diagram that illustrates example components of a highresolution (hi res) LIDAR system 200′. The system 200′ can be similar tothe system 200 with the exception of the features discussed herein. Thesystem 200′ can be a coherent LIDAR system that is constructed withmonostatic transceivers. The system 200′ can include the source 212 thattransmits the carrier wave 201 along a single-mode optical waveguide 225over a transmission path 222, through a circulator 226 and out a tip 217of the single-mode optical waveguide 225 that is positioned in a focalplane of a collimating optic 229. The tip 217 can be positioned within athreshold distance (e.g. about 100 μm) of the focal plane of thecollimating optic 229 or within a range from about 0.1% to about 0.5% ofthe focal length of the collimating optic 229. The collimating optic 229can include one or more of doublets, aspheres or multi-element designs.The carrier wave 201 exiting the optical waveguide tip 217 can be shapedby the optic 229 into a collimated target beam 205′ which is scannedover a range of angles 227 by scanning optics 218.

In some embodiments, the carrier wave 201 is phase or frequencymodulated in a modulator 282 a upstream of the collimation optic 229. Insome embodiments, modulator 282 is excluded. Return beams 291 from anobject can be directed by the scanning optics 218 and focused by thecollimation optics 229 onto the tip 217 so that the return beam 291 isreceived in the single-mode optical waveguide tip 217. The return beam291 can then redirected by the circulator 226 into a single mode opticalwaveguide along the receive path 224 and to optical mixers 284 where thereturn beam 291 is combined with the reference beam 207 b that isdirected through a single-mode optical waveguide along a localoscillator path 220. The system 200′ can operate under the principalthat maximum spatial mode overlap of the returned beam 291 with thereference signal 207 b will maximize heterodyne mixing (opticalinterference) efficiency between the returned signal 291 and thereference beam 207 b. This arrangement is advantageous as it can help toavoid challenging alignment procedures associated with bi-static LIDARsystems.

FIG. 2E is a block diagram that illustrates a side view of examplecomponents of a high resolution (hi res) LIDAR system 200″. FIG. 2F is ablock diagram that illustrates a top view of the example components ofthe high resolution (hi res) LIDAR system 200″ of FIG. 2E. The system200″ can be similar to the system 200′ with the exception of thefeatures discussed herein. The scanning optics 218 of the system 200″includes a first polygon scanner 244 a coupled to at least one motor(e.g., motor 257 shown in FIG. 2J) and configured to rotate at a firstangular velocity 249 a about a rotation axis 243. The scanning optics218 can include a second polygon scanner 244 b coupled to the at leastone motor and configured to rotate at a second angular velocity 249 babout the rotation axis 243. Although two polygon scanners 244 a, 244 bare depicted, more than two polygon scanners can be featured in thescanning optics 218. The at least one motor can include a first motorthat rotates the first polygon scanner 244 a and a second motor thatrotates the second polygon scanner 244 b. The first angular velocity 249a at which the first polygon scanner 244 a rotates can be a first fixedrotation speed. The second angular velocity 249 b at which the secondpolygon scanner 244 b rotates can be a second fixed rotation speed. Thesecond fixed rotation speed can be different (e.g. less than) the firstfixed rotation speed. The first fixed rotation speed of the firstangular velocity 249 a can be in a range from about 1000 revolutions perminute (rpm) to about 5000 rpm and the second fixed rotation speed ofthe second angular velocity 249 b is in a range from about 200 rpm toabout 1000 rpm. The first polygon scanner 244 a and second polygonscanner 244 b can rotate in different directions, such as oppositedirections (e.g., clockwise and counter-clockwise); for example, thefirst angular velocity 249 a and the second angular velocity 249 b canhave different directions (e.g. clockwise and counter-clockwise). Thescanners 244 a, 244 b may not be limited to the polygon scannersdepicted in FIGS. 2E-2F and may include any type of polygon scanner(e.g. prismatic, pyramidal, stepped geometries, etc.).

In an example embodiment, each polygon scanner 244 a, 244 b has one ormore of the following characteristics: manufactured by Blackmore®Sensors with Copal turned mirrors, has an inscribed diameter of about 2inches or in a range from about 1 inch to about 3 inches, each mirror isabout 0.5 inches tall or in a range from about 0.25 inches to about 0.75inches, has an overall height of about 2.5 inches or in a range fromabout 2 inches to about 3 inches, is powered by a three-phase BrushlessDirect Current (BLDC) motor with encoder pole-pair switching, has arotation speed in a range from about 1000 revolutions per minute (rpm)to about 5000 rpm, has a reduction ratio of about 5:1 and a distancefrom the collimator 229 of about 1.5 inches or in a range from about 1inch to about 2 inches. In some embodiments, the scanning optics 218 ofthe system 200″ use an optic other than the polygon scanners 244 a, 244b.

In some embodiments, one or more parameters of the polygon scanners 244a, 244 b are different from one another. A mass of the second polygonscanner 244 b can be greater than a mass of the first polygon scanner244 a. The outer diameter of the polygon scanners 244 a, 244 b can beabout equal but the first polygon scanner 244 a can have a larger bore(e.g. larger inner diameter) through which the rotation axis 243 isreceived, so that the mass of the first polygon scanner 244 a is lessthan the second polygon scanner 244 b. A ratio of the mass of the secondpolygon scanner 244 b to the mass of the first polygon scanner 244 a canbe about equal to the ratio of the rotation speed of the first angularvelocity 249 a to the rotation speed of the second angular velocity 249b. This advantageously ensures there is no net angular momentum betweenthe polygon scanners 244 a, 244 b during rotation due to inertialchanges, which can facilitate stability of the system 200″ duringoperation. The angular momentum and the moment of inertia of eachpolygon scanner 244 a, 244 b is provided by:

{right arrow over (L)}=I{right arrow over (ω)}  (5a)

I=mr²   (5b)

where L is the angular momentum of each polygon scanner 244 a, 244 b; Iis the moment of inertia of each polygon scanner 244 a, 244 b; ω is theangular velocity 249 a, 249 b; m is the mass of each polygon scanner 244a, 244 b and r is the radial distance of the mass m from the rotationaxis 243. In an embodiment, the first rotation speed of the firstangular velocity 249 a is greater than the second rotation speed of thesecond angular velocity 249 b and a ratio of the first rotation speed tothe second rotation speed is in a range from about 3 to about 10. Inthis embodiment, the mass of the second polygon scanner 244 b is greaterthan the mass of the first polygon scanner 244 a based on the same ratioof the first rotation speed to the second rotation speed. Thus, althoughthe moment of inertia I of the second polygon scanner 244 b is greaterthan that of the first polygon scanner 244 a, per equation 5b, themagnitude of the angular velocity (e.g. rotation speed) of the firstpolygon scanner 244 a is greater than the second polygon scanner 244 bby an equal magnitude and thus, the angular momentum L of the polygonscanners 244 a, 244 b is about equal in magnitude, per equation 5a andopposite in sign since the angular velocities 249 a, 249 b are oppositein direction. This advantageously ensures that there is no or negligiblenet angular momentum between the polygon scanners 244 a, 244 b duringoperation of the system 200″.

The system 200″ can include a scanner 241 positioned between thecollimator 229 and the scanning optics 218 (e.g. polygon scanners 244 a,244 b) that is configured to adjust a direction of the collimated beam205′ in a third plane 234 (e.g. plane of FIG. 2E). The scanner 241 canadjust the direction of the collimated beam 205′ between the firstpolygon scanner 244 a and the second polygon scanner 244 b. The scanner241 can adjust the beam 205′ as a scanned beam 233 between a facet 245a, 245 b of the first polygon scanner 244 a and a facet 245 a, 245 b ofthe second polygon scanner 244 b. The scanner 241 can continuously movethe scanned beam 233 between the facets 245 of the first polygon scanner244 a and the facets 245 of the second polygon scanner 244 b using atriangular waveform (e.g. five times per second).

When the scanner 241 directs the scanned beam 233 onto a facet 245 a,245 b of the first polygon scanner 244 a, the facet 245 a, 245 b candeflect the beam 233′ into a first plane 235 (e.g. plane of FIG. 2F)that is different from the third plane 234 (e.g. plane of FIG. 2E) inwhich the beam 233 is incident on the first polygon scanner 244 a. FIG.2J depicts the first plane 235 that defines a lower scan region 264where the beam 233′ is scanned from the first angle to the second angle.In an embodiment, the first plane 235 forms an angle of about 85 degreesor 105 degrees with the rotation axis 243 or an angle in a range fromabout 45 degrees to about 150 degrees or in a range from about 30degrees to about 150 degrees. In an embodiment, the second plane 237forms an angle of about 90 degrees with the rotation axis 243 or anangle in a range from about 60 degrees to about 120 degrees or in arange from about 40 degrees to about 150 degrees. In an embodiment,based on the rotation of the first polygon scanner 244 a about therotation axis 243, the scanned beam 233′ is deflected by the facet 245a, 245 b of the first polygon scanner 244 a from a first angle to asecond angle within the first plane 235 (e.g. plane of FIG. 2F). Thefirst plane 235 (e.g. plane of FIG. 2F) can be about orthogonal to thethird plane 234. For purposes of this description, orthogonal means arelative orientation defined by angle in a range of 90±20 degrees. Thescanner 241 can adjust the direction of the scanned beam 233 at a fixedscan speed sufficiently slow that the scanned beam 233′ is deflectedfrom the first angle to the second angle within the first plane 235 athreshold number (e.g. one) of times during the time period that thescanned beam 233 is directed on the first polygon scanner 244 a. Thescanner 241 can adjust the direction of the scanned beam 233 at a scanspeed to the facet 245 a, 245 b of the first polygon scanner 244 a andhold the position of the scanned beam 233 for a minimum time period sothat the scanned beam 233′ is deflected from the first angle to thesecond angle within the first plane 235 a threshold number (e.g. one) oftimes.

In an embodiment, when the scanner 241 directs the scanned beam 233 fromthe first polygon scanner 244 a onto a facet 245 a, 245 b of the secondpolygon scanner 244 b, the facet 245 a, 245 b deflects the beam 233′into a second plane 237 that is different from the third plane 234 (e.g.plane of FIG. 2E) in which the beam 233 is incident on the secondpolygon scanner 244 b and is different from the first plane 235. FIG. 2Jdepicts the second plane 237 that defines an upper scan region 262 of ascan region 261 (see FIG. 2K) where the beam 233′ is scanned from thefirst angle to the second angle. In some embodiments, the upper scanregion 262 and lower scan region 264 of the scan region 261 have anoverlapping region 263. In some embodiments, the upper scan region 262and lower scan region 264 do not overlap and thus there is nooverlapping region 263. In an embodiment, the second plane 237 forms anangle of about 90 degrees with the rotation axis 243. In an embodiment,based on the rotation of the second polygon scanner 244 b about therotation axis 243, the scanned beam 233′ is deflected by the facet 245a, 245 b of the second polygon scanner 244 b from a first angle to asecond angle within the second plane 237 (e.g. plane of FIG. 2F). Adirection of the second angular velocity 249 b can be opposite to thedirection of first angular velocity 249 a and thus the beam 233′ iscounter scanned in the second plane 237 in an opposite direction (e.g.from the second angle to the first angle) as compared to the beam 233′scanned in the first plane 235 (e.g. from the first angle to the secondangle). The second plane 237 (e.g. plane of FIG. 2F) can be aboutorthogonal to the third plane 234. The scanner 241 can adjust thedirection of the scanned beam 233 at a fixed scan speed sufficientlyslow that the scanned beam 233′ is deflected from the first angle to thesecond angle within the second plane 237 a threshold number (e.g. one)of times during the time period that the scanned beam 233 is directed onthe second polygon scanner 244 b. The scanner 241 can adjust thedirection of the scanned beam 233 at a scan speed to the facet 245 a,245 b of the second polygon scanner 244 b and hold the position of thescanned beam 233 for a minimum time period so that the scanned beam 233′is deflected from the first angle to the second angle within the secondplane 237 a threshold number (e.g. one) of times.

FIG. 2I is a schematic diagram that illustrates an exploded view of anexample of the scanning optics 218 of the system 200″ of FIG. 2E. In anembodiment, the scanning optics 218 includes the first polygon scanner244 a, which can be coupled to the motor 257, and the second polygonscanner 244 b, which can be coupled to the motor 257 through the firstpolygon scanner 244 a. The first polygon scanner 244 a can be rotatablymounted to a drive shaft 258 and a planetary bearing 259 of the motor257. The first polygon scanner 244 a can include a recess (not shown) toreceive the drive shaft 258 and planetary bearing 259. The secondpolygon scanner 244 b can be rotatably mounted to the first polygonscanner 244 a with planetary transmission gears 254 and a driver sungear 256 that are positioned within a ring gear 252. The ring gear 252can be received within a cavity (not shown) on an undersurface of thesecond polygon scanner 244 b. One or more parameters of the gears 254,256 and/or ring gear 252 (e.g. diameter, quantity, etc.) can be selectedto adjust a ratio of a magnitude of the rotation speed of the firstangular velocity 249 a of the first polygon scanner 244 a to a magnitudeof the rotation speed of the second angular velocity 249 b of the secondpolygon scanner 244 b. For example, the ratio can be in a range fromabout 3 to about 10 or in a range from about 2 to about 20. The motor257 can be manufactured by Nidec Copal® Electronics, Inc. of Torrance,Calif. The transmission (e.g. gears 254, 256 and ring 252) can beprovided by SDP/SI® gears including S1EO5ZM05S072 internal ring gearcoupled with selections from ground metric spur gear offerings.

Although the motor 257 in FIG. 2I causes both of the polygon scanners244 a, 244 b to move at the same time (e.g. in opposite directions), asdepicted in FIGS. 2E-2F the beam 233 may be only directed by the scanner241 onto one polygon scanner 244 a, 244 b at a time, so that the beam233′ is scanned through the first plane 235 over the lower scan region264 over a first time period and is subsequently scanned through thesecond plane 237 over the upper scan region 262 over a second timeperiod after the first time period.

FIG. 2G is a block diagram that illustrates a side view of examplecomponents of a high resolution (hi res) LIDAR system 200″, according toan embodiment. FIG. 2H is a block diagram that illustrates a top view ofthe example components of the high resolution (hi res) LIDAR system 200″of FIG. 2G, according to an embodiment. The system 200″ of FIGS. 2G-2Hcan be similar to that described with reference to FIGS. 2E-2F, with theexception of the features discussed herein. Unlike the embodiment ofFIGS. 2E-2F where a single waveguide 225 and a single collimator 229provide a single collimated beam 205′ that is scanned by the scanner 241between the first polygon scanners 244 a to the second polygon scanner244 b, the system 200″ of FIGS. 2G-2H includes a pair of waveguides 225a, 225 b and a pair of collimators 229 a, 229 b that respectivelyprovide a pair of collimated beams 205′ to the first and second polygonscanners 244 a, 244 b. In an embodiment, the system 200″ of FIGS. 2G-2Hexcludes the scanner 241. The beam 201 from the laser source 212 may besplit by a beam splitter (not shown) into two beams 201 that aredirected into the waveguides 225 a, 225 b. The system 200″ can includetwo circulators 226 and two receiving waveguides in the receive path 224to accommodate separate return beams 291 from the respective polygonscanners 244 a, 244 b that are received at the tips of the respectivewaveguides 225 a, 225 b. The system 200″ of FIGS. 2G-2H can include twolaser sources 212 and each waveguide 225 a, 225 b can receive arespective beam 201 from one of the laser sources 212. The system 200″can also include two circulators 226 and two receiving waveguides toprocess separate return beams 291 from the polygon scanners 244 a, 244b. The system 200″ of FIGS. 2G-2H can accommodate simultaneous scanningof the beam 233′ in the first and second plane 235, 237 and thus in theupper scan region and lower scan region 262, 264 (e.g. in oppositedirections) since the system 200″ includes two processing channels toaccommodate simultaneous return beams 291 from the polygon scanners 244a, 244 b.

4. Monostatic Coherent LIDAR System Parameters

In an embodiment, monostatic coherent LIDAR performance of the system200′, 200″ is modeled by including system parameters in a so called“link budget”. A link budget estimates the expected value of the signalto noise ratio (SNR) for various system and target parameters. On thesystem side, a link budget can include one or more of output opticalpower, integration time, detector characteristics, insertion losses inwaveguide connections, mode overlap between the imaged spot and themonostatic collection waveguide, and optical transceivercharacteristics. On the target side, a link budget can include one ormore of atmospheric characteristics, target reflectivity, and targetrange.

FIG. 4A is a graph that illustrates an example signal-to-noise ratio(SNR) versus target range for the return beam 291 in the system 200′ ofFIG. 2D or systems 200″ of FIGS. 2E-2H without scanning, according to anembodiment. In other embodiments, FIG. 4A depicts an example of SNRversus target range for the return beam 291 in the system 200 of FIG.2A. The horizontal axis 402 is target range in units of meters (m). Thevertical axis 404 is SNR in units of decibels (dB). A curve 410 depictsthe values of SNR versus range that is divided into a near field 406 anda far field 408 with a transition from the near field 406 of the curve410 with a relatively flat slope to the far field 408 of the curve 410with a negative slope (e.g. about −20 dB per 10 m). The reduction in SNRin the far field 408 is dominated by “r-squared” losses, since thescattering atmosphere through which the return beam 291 passes growswith the square of the range to the target while the surface area of theoptical waveguide tip 217 to collect the return beam 291 is fixed. FIG.4B is a graph that illustrates an example of a curve 411 indicating1/r-squared loss that drives the shape of the SNR curve 410 in the farfield 408, according to an embodiment. The horizontal axis 402 is rangein units of meters (m) and the vertical axis 407 is power loss that isunitless.

In the near field 406, a primary driver of the SNR is a diameter of thecollimated return beam 291 before it is focused by the collimationoptics 229 to the tip 217. FIG. 4C is a graph that illustrates anexample of collimated beam diameter versus range for the return beam 291in the system 200′ of FIG. 2D or system 200″ of FIGS. 2E-2H withoutscanning, according to an embodiment. The horizontal axis 402 is targetrange in units of meters (m) and the vertical axis 405 is diameter ofthe return beam 291 in units of meters (m). In an embodiment, curve 414depicts the diameter of the collimated return beam 291 incident on thecollimation optics 229 prior to the return beam 291 being focused to thetip 217 of the optical waveguide. The curve 414 illustrates that thediameter of the collimated return beam 291 incident on the collimationoptics 229 increases with increasing target range.

In an embodiment, in the near field 406, as the diameter of thecollimated return beam 291 grows at larger target ranges, a diameter ofthe focused return beam 291 by the collimation optics 229 at the tip 217shrinks. FIG. 4D is a graph that illustrates an example of SNRassociated with collection efficiency of the return beam 291 at the tip217 versus range for the transmitted signal in the system of FIG. 2D orFIGS. 2E-2H without scanning, according to an embodiment. The horizontalaxis 402 is target range in units of meters (m) and the vertical axis404 is SNR in units of decibels (dB). The curve 416 depicts the nearfield SNR of the focused return beam 291 by the collimation optics 229at the tip 217 based on target range. At close ranges within the nearfield 406, an image 418 a of the focused return beam 291 at the tip 217by the collimation optics 229 is sufficiently larger than the core sizeof the single mode optical fiber tip 217. Thus the SNR associated withthe collection efficiency is relatively low. At longer ranges within thenear field 406, an image 418 b of the focused return beam 291 at the tip217 by the collimation optics 229 is much smaller than the image 418 aand thus the SNR attributable to the collection efficiency increases atlonger ranges. In an embodiment, the curve 416 demonstrates that the SNRin near field 406 has a positive slope (e.g. +20 dB per 10 meters) basedon the improved collection efficiency of the focused return beam 291 atlonger ranges. In one embodiment, this positive slope in the near fieldSNR cancels the negative slope in the near field SNR discussed in FIG.4B that is attributable to “r-squared” losses and thus leads to therelatively flat region of the SNR curve 410 in the near field 406. Thepositive slope in the SNR curve 416 in FIG. 4D does not extend into thefar field 408 and thus the “r-squared” losses of FIG. 4B dominate thefar field 408 SNR as depicted in the SNR curve 410 in the far field 408.

While the discussion in relation to FIGS. 4A-4D predicts SNR of thereturn beam 291 as a function of the target range, the predicted SNR inFIGS. 4A-4D does not fully characterize the performance of the scannedmonostatic coherent LIDAR system 200′, 200″ since it does not consider ascan rate of the scanning optics 218. In an embodiment, due to roundtrip delay of the return beam 291, the receive mode of the return beam291 will laterally shift or “walk off” from the transmitted mode of thetransmitted beam 205′ when the beam is being scanned by the scanningoptics 218. FIG. 4E illustrates an example of beam walkoff for varioustarget ranges and scan speeds in the system 200′ of FIG. 2D or system200″ of FIGS. 2E-2H (e.g. fixed scan speeds of polygon scanners 244 a,244 b), according to an embodiment. The horizontal axis 402 is targetrange and the vertical axis 422 is scan speed of the beam using thescanning optics 218. As FIG. 4E depicts, there is no beam walkoff whenthe beam is not scanned (bottom row) since the image 418 a of thefocused return beam 291 is centered on the fiber tip 217 demonstratingno beam walkoff at short target range and the image 418 b of the focusedreturn beam 291 is also centered on the fiber tip 217 demonstrating nobeam walkoff at far target range. When the beam is scanned at a moderatescan speed (middle row in FIG. 4E), a moderate beam walkoff 419 a isobserved between the image 418 a of the focused return beam 291 and thefiber tip 217 and a larger beam walkoff 419 b is observed between theimage 418 b of the focused return beam 291 and the fiber tip 217. Whenthe beam is scanned at a high scan speed (top row in FIG. 4E), a beamwalkoff 421 a is observed at short range that exceeds the beam walkoff419 a at the moderate scan speed and a beam walkoff 421 b is observed atlarge range that exceeds the beam walk off 419 b at the moderate scanspeed. Thus, the beam walkoff increases as the target range and scanspeed increase. In an embodiment, increased target range induces a timedelay during which the image 418 a, 418 b shifts away from the tip 217of the fiber core. Thus a model of the mode overlap accounts thiswalkoff appropriately. In one embodiment, such a model should limit thebeam walkoff 419 based on a diameter of the image 418 (e.g. no greaterthan half of the diameter of the image 418).

FIG. 4F is a graph that illustrates an example of coupling efficiencyversus target range for various scan rates in the system 200′ of FIG. 2Dor system 200″ of FIGS. 2E-2H, according to an embodiment. Thehorizontal axis 402 is target range in units of meters (m) and thevertical axis 430 is coupling efficiency which is unitless. In anembodiment, the coupling efficiency is inversely proportional to thebeam walkoff 419. A first curve 432 a depicts the coupling efficiency ofthe focused return beam 291 into the fiber tip 217 for various targetranges based on no scanning of the beam. The coupling efficiency remainsrelatively high and constant for a wide range of target ranges. A secondcurve 432 b depicts the coupling efficiency of the focused return beam291 into the fiber tip 217 for various target ranges based on moderatescan rate of the beam. In an embodiment, the coupling efficiency at themoderate scan rate peaks at a moderate target range (e.g. about 120 m)and then decreases as target range increases. A third curve 432 cdepicts the coupling efficiency of the focused return beam 291 into thefiber tip 217 for various target ranges based on a high scan rate of thebeam. In an embodiment, the coupling efficiency of the high scan ratepeaks at a low target range (e.g. about 80 m) and then decreases astarget range increases.

Based on the curves in FIG. 4F, scanning too fast can eventually make itimpossible to see beyond some target range. In this instance, the image418 b of the focused return beam 291 does not couple into the fiber tip217 and instead has totally walked off the receiver mode of the tip 217.FIG. 4G is a graph that illustrates an example of SNR versus targetrange for various scan rates in the system 200′ of FIG. 2D or system200″ of FIGS. 2E-2H, according to an embodiment. The horizontal axis 402is target range in units of meters (m) and the vertical axis 404 is SNRin units of decibels (dB). A first curve 440 a depicts the SNR of thefocused return beam 291 on the fiber tip 217 based on target range wherethe beam is not scanned. A second curve 440 b depicts the SNR of thefocused return beam 291 on the fiber tip 217 based on target range wherethe beam is scanned at a moderate scan rate. In an example embodiment,the moderate scan rate is about 2500 degrees per sec (deg/sec) or in arange from about 1000 deg/sec to about 4000 deg/sec or in a range fromabout 500 deg/sec to about 5000 deg/sec. A third curve 440 c depicts theSNR of the focused return beam 291 on the fiber tip 217 based on targetrange where the beam is scanned at a high scan rate. In an exampleembodiment, the high scan rate is about 5500 deg/sec or in a range fromabout 4000 deg/sec to about 7000 deg/sec or in a range from about 3000deg/sec to about 8000 deg/sec. In an embodiment, the moderate scan rateand high scan rate are based on a beam size and goal of the system. Inan embodiment, the moderate scan rate and high scan rate are based onthe gearing structure of the scanning optics 218 in FIG. 21, e.g. thepolygon scanner 244 a rotates at the high scan rate and the polygonscanner 244 b rotates at the moderate scan rate where the ratio of thehigh scan rate to the moderate scan rate is based on the structure ofthe gears in FIG. 2I. In an example embodiment, the numerical ranges ofthe moderate scan rate and high scan rate above are based on acollimated beam with a diameter of about 1 centimeter (cm) used to scanan image out to a maximum target range of about 200 meters (m).

In addition to the scan rate of the beam, the SNR of the return beam 291is affected by the integration time over which the acquisition system240 and/or processing system 250 samples and processes the return beam291. In some embodiments, the beam is scanned between discrete anglesand is held stationary or almost stationary at discrete angles in theangle range 227 for a respective integration time at each discreteangle. The SNR of the return beam 291 is affected by the value of theintegration time and the target range. As previously discussed, thecross sectional area of the beam increases with target range resultingin increased atmospheric scattering and thus an intensity of the returnbeam 291 decreases with increasing range. Accordingly, a longerintegration time is needed to achieve the same SNR for a return beam 291from a longer target range.

FIG. 4H is a graph that illustrates an example of SNR versus targetrange for various integration times in the system 200′ of FIG. 2D orsystem 200″ of FIGS. 2E-2H, according to an embodiment. The horizontalaxis 402 is target range in units of meters (m) and the vertical axis404 is SNR in units of decibels (dB). A first curve 450 a depicts SNRvalues of the return beam 291 over the target range, where the system200′, 200″ is set to a first integration time (e.g. 3.2 μs). A secondcurve 450 b depicts SNR values of the return beam 291 over the targetrange, where the system 200′, 200″ is set to a second integration time(e.g. 1.6 μs). A third curve 450 c depicts SNR values of the return beam291 over the target range, where the system 200′, 200″ is set to a thirdintegration time (e.g. 800 ns). A fourth curve 450 d depicts SNR valuesof the return beam 291 over the target range, where the system 200′,200″ is set to a fourth integration time (e.g. 400 ns). The curves 450demonstrate that for a fixed target range, an increased SNR is achievedwith increasing integration time. The curves 450 also demonstrate thatfor a fixed integration time, the SNR of the return beam 291 decreaseswith increased range for the reasons previously discussed. In anembodiment, the LIDAR system 200″ selects a fixed integration time (e.g.1.6 μs) for the scanning at the range of angles 227 and resulting targetranges, so that the SNR associated with the fixed integration timeexceeds an SNR threshold 452 over the target range. In some embodiments,the system 200″ minimizes the integration time at each angle within therange of angles 227 using the target range at each angle, so to minimizethe integration time over the range of angles 227. FIG. 4I is a graphthat illustrates an example of a measurement rate versus target range inthe system 200′ of FIG. 2D or system 200″ of FIGS. 2E-2H, according toan embodiment. The horizontal axis 402 is target range in units ofmeters (m) and the vertical axis 474 is number of allowable measurementsper unit time in units of number of allowable measurements per second.Curve 476 depicts the number of allowable measurements per second ateach target range. In an embodiment, curve 476 represents an inverse ofthe integration time, e.g. the number of return beams 291 that can bedetected at each target range per second whereas integration timeconveys how long it takes to process the return beam 291 at each targetrange. Curve 478 is also provided and is a good target of the number ofallowable measurements per second at each target range. The curve 478 isbased on power of 2 intervals for a given ADC (analog to digitalconversion) rate. Curve 478 represents a good target of the number ofallowable measurements per second since when the number of digitizedsamples is a power of 2, the fast fourier transform on such a lengthsignal is more efficient.

5. Vehicle Control Overview

In some embodiments a vehicle is controlled at least in part based ondata received from a hi-res Doppler LIDAR system mounted on the vehicle.

FIG. 3A is a block diagram that illustrates an example system 301 thatincludes at least one hi-res Doppler LIDAR system 320 mounted on avehicle 310, according to an embodiment. The LIDAR system 320 canincorporate features of the LIDAR systems 200, 200′, 200″. The vehiclehas a center of mass indicted by a star 311 and travels in a forwarddirection given by arrow 313. In some embodiments, the vehicle 310includes a component, such as a steering or braking system (not shown),operated in response to a signal from a processor, such as the vehiclecontrol module 272 of the processing system 250. In some embodiments thevehicle has an on-board processor 314, such as chip set depicted in FIG.8. In some embodiments, the on board processor 314 is in wired orwireless communication with a remote processor, as depicted in FIG. 7.In an embodiment, the processing system 250 of the LIDAR system iscommunicatively coupled with the on-board processor 314 or theprocessing system 250 of the LIDAR is used to perform the operations ofthe on board processor 314 so that the vehicle control module 272 causesthe processing system 250 to transmit one or more signals to thesteering or braking system of the vehicle to control the direction andspeed of the vehicle. The hi-res Doppler LIDAR uses a scanning beam 322that sweeps from one side to another side, represented by future beam323, through an azimuthal field of view 324, as well as through verticalangles (FIG. 3B) illuminating spots in the surroundings of vehicle 310.In some embodiments, the field of view is 360 degrees of azimuth. Insome embodiments the inclination angle field of view is from about +10degrees to about −10 degrees or a subset thereof. In an embodiment, thefield of view 324 includes the upper scan region 262 and lower scanregion 264. In this embodiment, the scanning beam 322 is scanned in asimilar manner as the beam 233′ in the system 200″ of FIGS. 2E-2F orFIGS. 2G-2H, e.g. the scanning beam 322 is scanned over the field ofview 324 in the upper scan region 262 by the second polygon scanner 244b and the scanning beam 322 is also scanned over the field of view 324in the lower scan region 264 by the first polygon scanner 244 a. In oneexample embodiment, such as the system 200″ of FIGS. 2E-2F, the scanningbeam 322 is scanned over the upper scan region 262 and lower scan region264 at separate time periods. In another example embodiment, as such asthe system of FIGS. 2G-2H, the scanning beam 322 is simultaneouslyscanned over the upper scan region 262 and lower scan region 264. Inanother example embodiment, the scanning beam 322 is scanned in oppositedirections (counter scan) over the upper scan region 262 and lower scanregion 264.

In some embodiments, the vehicle includes ancillary sensors (not shown),such as a GPS sensor, odometer, tachometer, temperature sensor, vacuumsensor, electrical voltage or current sensors. In some embodiments, agyroscope 330 is included to provide rotation information.

FIG. 3B is a block diagram that illustrates an example system 301′ thatincludes at least one hi-res LIDAR system 320 mounted on the vehicle310, according to an embodiment. The LIDAR system 320 can incorporatefeatures of the system 200 or system 200′. The vehicle 310 can move overthe surface 349 (e.g. road) with the forward direction based on thearrow 313. In an embodiment, the first plane 235 is depicted thatdefines the lower scan region 264 that the beam 233′ is scanned by thepolygon scanner 244 a from the first angle to the second angle.Additionally, the second plane 237 is depicted that defines the upperscan region 262 that the beam 233′ is scanned by the polygon scanner 244b from the first angle to the second angle. In an embodiment, the system200″ can be used to scan the beam 233′ over a first plane 235′ thatintersects a ceiling 347. In this example embodiment, the scanningoptics 218 is inverted from the arrangement depicted in FIG. 2J suchthat the first polygon scanner 244 a is positioned above the secondpolygon scanner 244 b and the first polygon scanner 244 scans the beamover the first plane 235′. In one embodiment, the first planes 235, 235′are not aligned with the surface 349 and the ceiling 347 and instead areoriented within an angle range (e.g. within ±10 degrees of the arrow 313and/or within ±10 degrees of the second plane 237).

In designing the system 301′, a predetermined maximum design range ofthe beams at each plane 235, 237 can be determined and can represent amaximum anticipated target range at each plane 235, 237. In oneembodiment, the predetermined maximum design range is a fixed value orfixed range of values for each plane 235, 237. In an embodiment, thefirst plane 235 is oriented toward the surface 349 and intersects thesurface 349 within some maximum design range from the vehicle 310. Thus,for the first plane 235 the system 320 does not consider targetspositioned beyond the surface 349. In an example embodiment, the firstplane 235 forms an angle that is about −15 degrees or in a range fromabout −25 degrees to about −10 degrees with respect to the arrow 313 andthe maximum design range is about 4 meters (m) or within a range fromabout 1 m to about 10 m or in a range from about 2 m to about 6 m. In anembodiment, the first plane 235′ is oriented toward the sky andintersects a ceiling 347 within some maximum design range from thevehicle 310. Thus, for the first plane 235′ the system 320 does notconsider targets positioned above the ceiling 347. In an exampleembodiment, the ceiling 347 is at an altitude of about 12 m or in arange from about 8 m to about 15 m from the surface 349 (e.g. thatdefines an altitude of 0 m), the first plane 235′ forms an angle ofabout 15 degrees or in a range from about 10 degrees to about 20 degreeswith respect to the arrow 313 and the maximum design range is about 7 mor within a range from about 4 m to about 10 m or within a range fromabout 1 m to about 15 m.

In an embodiment, the second plane 237 is oriented about parallel withthe arrow 313 and intersects a target 343 positioned at a maximum designrange from the vehicle 310. In one example embodiment, FIG. 3B is notdrawn to scale and target 343 is positioned at a much further distancefrom the vehicle 310 than depicted. For purposes of this description,“about parallel” means within about ±10 degrees or within about ±15degrees of the arrow 313. In an example embodiment, the maximum designrange of the target 343 in the second plane 237 is about 200 m or withina range from about 150 m to about 300 m or within a range from about 100m to about 500 m.

6. Method for Optimization of Scan Pattern in Coherent LIDAR System

FIG. 5 is a flow chart that illustrates an example method 500 foroptimizing a scan pattern of a LIDAR system on an autonomous vehicle.Although steps are depicted in FIGS. 5 and 6 as integral steps in aparticular order for purposes of illustration, one or more steps, orportions thereof, can be performed in a different order, or overlappingin time, in series or in parallel, or are omitted, or one or moreadditional steps are added, or the method is changed in some combinationof ways.

In step 501, data is received on a processor that indicates first SNRvalues of a signal reflected by a target and detected by the LIDARsystem based on values of a range of the target, where the first SNRvalues are for a respective value of a scan rate of the LIDAR system. Inan embodiment, in step 501 the data is first SNR values of the focusedreturn beam 291 on the fiber tip 217 in the system 200″. In oneembodiment, the data includes values of curve 440 a and/or curve 440 band/or curve 440 c that indicate SNR values of the return beam 291,where each curve 440 is for a respective value of the scan rate of thebeam. In some embodiments, the data is not limited to curves 440 a, 440b, 440 c and includes SNR values of less or more curves than aredepicted in FIG. 4G, where each SNR curve is based on a respective valueof the scan rate. In some embodiments, the data includes SNR values thatcould be used to form the curve over the target range for eachrespective value of the scan rate. In an example embodiment, in step 501the data is stored in a memory of the processing system 250 and each setof first SNR values is stored with an associated value of the scan rateof the LIDAR system. In one embodiment, in step 501 the first SNR valuesare obtained over a range from about 0 meters to about 500 meters (e.g.automotive vehicles) or within a range from about 0 meters to about 1000meters (e.g. airborne vehicles) and for scan rate values from about 2000deg/sec to about 6000 deg/sec or within a range from about 1000deg/second to about 7000 deg/sec In some embodiments, the first SNRvalues are predetermined and are received by the processor in step 501.In other embodiments, the first SNR values are measured by the LIDARsystem and subsequently received by the processor in step 501. In oneembodiment, the data is input in step 501 using an input device 712and/or uploaded to the memory 704 of the processing system 250 over anetwork link 778 from a local area network 780, internet 790 or externalserver 792.

In step 503, data is received on a processor that indicates second SNRvalues of a signal reflected by a target and detected by the LIDARsystem based on values of a range of the target, where the second SNRvalues are for a respective value of an integration time of the LIDARsystem. In an embodiment, in step 503 the data is second SNR values ofthe focused return beam 291 in the system 200″ for a respectiveintegration time over which the beam is processed by the acquisitionsystem 240 and/or processing system 250. In one embodiment, the dataincludes values of curve 450 a and/or curve 450 b and/or curve 450 cand/or curve 450 d that indicate SNR values of the return beam 291,where each curve 450 is for a respective value of the integration timethat the beam is processed by the acquisition system 240 and/orprocessing system 250. In some embodiments, the data is not limited tocurves 450 a, 450 b, 450 c, 450 d and includes less or more curves thanare depicted in FIG. 4H, where each SNR curve is based on a respectivevalue of the integration time. In some embodiments, the data need not bea curve and instead is the SNR values used to form the curve over thetarget range for each respective value of the integration time. In anexample embodiment, in step 503 the data is stored in a memory of theprocessing system 250 and each set of second SNR values is stored withan associated value of the integration time of the LIDAR system. In oneembodiment, in step 503 the second SNR values are obtained over a rangefrom about 0 meters to about 500 meters (e.g. automotive vehicles) orfrom a range from about 0 meters to about 1000 meters (e.g. airbornevehicles) and for integration time values from about 100 nanosecond (ns)to about 5 microseconds (μs). In some embodiments, the second SNR valuesare predetermined and are received by the processor in step 503. In someembodiments, the second SNR values are measured by the LIDAR system andsubsequently received by the processor in step 503. In one embodiment,the data is input in step 503 using an input device 712 and/or uploadedto the memory 704 of the processing system 250 over a network link 778from a local area network 780, internet 790 or external server 792.

In step 505, data is received on a processor that indicates the firstangle and the second angle that defines the angle range 324. In oneembodiment, in step 505 the first angle and the second angle define theangle range 324 (e.g. where the first and second angle are measured withrespect to arrow 313) of the lower scan region 264 defined by the firstplane 235. In another embodiment, in step 505 the first angle and thesecond angle define the angle range 324 of the upper scan region 262defined by the second plane 237. In an embodiment, the first angle andsecond angle are symmetric with respect to the arrow 313, e.g. the firstangle and the second angle are equal and opposite to each other. In anembodiment, the first angle and the second angle are about ±60 degreeswith respect to the arrow 313, e.g. ±60 degrees with respect to thearrow 313 defines the angle range 324. In some embodiments, the firstand second angle are about ±30 degrees, about ±40 degrees and about ±50degrees with respect to the arrow 313. In one embodiment, steps 501, 503and 505 are simultaneously performed in one step where the data in steps501, 503 and 505 is received at the processor in one simultaneouslystep.

In step 507, data is received on a processor that indicates the maximumdesign range of the target along each plane 235, 237 that defines theupper and lower scan regions 262, 264. In an embodiment, the maximumdesign range received in step 507 is a fixed value or fixed range ofvalues for each plane 235, 237 that defines the upper and lower scanregion 262, 264. In one embodiment, in step 507 the maximum design rangefor the first plane 235 is in a range from about 1 m to about 15 m orfrom about 4 m to about 10 m. In some embodiments, in step 507 themaximum design range for the second plane 237 is in a range from about150 m to about 300 m or in a range from about 100 m to about 400 m.

In one example embodiment, the data in step 507 is input using an inputdevice 712 (e.g. mouse or pointing device 716) and/or are uploaded tothe processing system 250 over a network link 778. In some embodiments,the maximum design range is predetermined and received during step 507.In some embodiments, the system 200, 200′, 200″ is used to measure themaximum design range at each plane 235, 237 and the maximum design rangeat each plane 235, 237 is subsequently received by the processing system250 in step 507.

In step 509, a maximum scan rate of the LIDAR system is determined atthe first plane 235 so that the SNR of the LIDAR system is greater thana minimum SNR threshold. At the first plane 235, the maximum designrange for that plane is first determined based on the received data instep 507. First SNR values received in step 501 are then determined forthe maximum design range at the plane 235 and it is further determinedwhich of these first SNR values exceed the minimum SNR threshold. In oneembodiment, values of curves 440 a, 440 b, 440 c are determined for amaximum design range (e.g. about 120 m) and it is further determinedthat the values of curves 440 a, 440 b exceeds the minimum SNR threshold442. Among those first SNR values which exceed the minimum SNRthreshold, the first SNR values with the maximum scan rate is selectedand the maximum scan rate is determined in step 509 for the plane 235.In the above embodiment, among the values of the curves 440 a, 440 bwhich exceeds the minimum SNR threshold 442 at the maximum design range(e.g. about 120 m), the curve 440 b values are selected as the maximumscan rate and the maximum scan rate (e.g. moderate scan rate associatedwith curve 440 b) is determined in step 509 for the plane 235. In step511, step 509 is repeated but the maximum scan rate is determined forthe second plane 237.

In an embodiment, FIG. 4G depicts that the maximum scan rate determinedin step 509 for the first plane 235 with a smaller maximum design range(e.g. fast scan rate based on curve 440 c) is greater than the maximumscan rate for second plane 237 with a larger maximum design range (e.g.moderate scan rate based on curve 440 b) determined in step 511. Thus,the rotation speed of the first polygon scanner 244 a (e.g. scans thebeam 233′ in the first plane 235 along the lower scan region 264) is setto be larger than the rotation speed of the second polygon scanner 244 b(e.g. scans the beam 233′ in the second plane 237 along the upper scanregion 262). In an example embodiment, the gearing structure of thescanning optics 218 (FIG. 2I) is arranged so that the ratio of therotation speed of the first polygon scanner 244 a to the rotation speedof the second polygon scanner 244 b has the appropriate value based onsteps 509, 511. In an embodiment, the step of determining the maximumscan rate in steps 509 and 511 ensures that beam walkoff 419 (FIG. 4E)of the return beam 291 on the fiber tip 217 is less than a ratio of adiameter of the image 418 of the return beam 291 on the tip 217. In anexample embodiment, the ratio is about 0.5 or in a range from about 0.3to about 0.7.

In step 513, a minimum integration time of the LIDAR system isdetermined at the first plane 235 so that the SNR of the LIDAR system isgreater than a minimum SNR threshold. At the first plane 235, themaximum design range for that plane is first determined based on thereceived data in step 507. Second SNR values received in step 503 arethen determined for the maximum design range at the plane 235 and it isfurther determined which of these second SNR values exceed the minimumSNR threshold. In one embodiment, values of curves 450 a, 450 b, 450 c,450 d are determined for a maximum design range (e.g. about 120 m) andit is further determined that the values of curves 450 a, 450 b, 450 cexceeds the minimum SNR threshold 452. Among those second SNR valueswhich exceed the minimum SNR threshold, the second SNR values with theminimum integration time is selected and the minimum integration time isdetermined in step 513 for that plane 235. In the above embodiment,among the values of the curves 450 a, 450 b, 450 c which exceeds theminimum SNR threshold 452 at the maximum design range (e.g. about 120m), the curve 450 c values are selected with the minimum integrationtime and the minimum integration time (e.g. about 800 ns) is determinedin step 511 for the plane 235. Step 515 involves repeating step 513 todetermine the minimum integration time for the second plane 237.

In step 517, a scan pattern of the lower scan region 264 in the LIDARsystem is defined based on the maximum scan rate from step 509 and theminimum integration time from step 513. In an embodiment, the maximumscan rate and the minimum integration time are fixed over the lower scanregion 264. In an example embodiment, the scan pattern is stored in amemory (e.g. memory 704) of the processing system 250. In step 519, thescan pattern of the upper scan region 262 is defined based on themaximum scan rate from step 511 and the minimum integration time fromstep 515.

In step 521, the LIDAR system is operated according to the scan patterndetermined in steps 517 and 519. In an embodiment, in step 519 the beamof the LIDAR system is scanned in the field of view 324 over the lowerscan region 264 and the upper scan region 262. In some embodiments, step521 involves using the system 200″ of FIGS. 2E-2F and scanning the beam233′ over the lower scan region 264 followed by the upper scan region262 as the scanner 241 moves the beam 233 from the first polygon scanner244 a to the second polygon scanner 244 b. In another embodiment, step521 involves using the system 200″ of FIGS. 2G-2H and simultaneouslyscanning the beams 233′ over the lower scan region 264 and upper scanregion 262. In an embodiment, in step 521 the beam 233′ is counterscanned over the upper scan region 262 and lower scan region 264 sincethe beam 233′ is scanned in opposite directions. This advantageouslyimproves the net resulting moment due to inertial changes of thescanning optics 218 during step 521 due to the counter rotation of thescanners 244 a, 244 b. In an embodiment, in step 521 the beam is scannedthrough the upper scan region 262 and lower scan region 264 over one ormore cycles, where the scan rate of the beam in each region 262, 264 isthe maximum scan rate in the scan pattern for that region 262, 264 (e.g.plane 235, 237) and the integration time of the LIDAR system at eachregion 262, 264 is the minimum integration time for that region 262, 264(e.g. plane 235, 237).

During or after step 521, the processor can operate the vehicle 310based at least in part on the data collected by the LIDAR system duringstep 521. In one embodiment, the processing system 250 of the LIDARsystem and/or the processor 314 of the vehicle 310 transmit one or moresignals to the steering and/or braking system of the vehicle based onthe data collected by the LIDAR system in step 521. In one exampleembodiment, the processing system 250 transmits one or more signals tothe steering or braking system of the vehicle 310 to control a positionof the vehicle 310 in response to the LIDAR data. In some embodiments,the processing system 250 transmits one or more signals to the processor314 of the vehicle 310 based on the LIDAR data collected in step 521 andthe processor 314 in turn transmits one or more signals to the steeringand braking system of the vehicle 310.

FIG. 6 is a flow chart that illustrates an example method 600 foroperating a LIDAR system 200″ on an autonomous vehicle, according to anembodiment. In step 601, the beam 201 is generated from the laser source212. In an embodiment, in step 601 the beam 201 is coupled into thetransmission waveguide 225 and transmitted from the tip 217 of thewaveguide 225. In some embodiments, in step 601 the beam 201 is splitusing a beam splitter (not shown) and the separate beams are directedinto the waveguides 225 a, 225 b and are transmitted from tips 217 ofthe waveguides 225 a, 225 b. In some embodiments, in step 601 two lasersources 212 are provided and each laser source 212 generates arespective beam 201 that is directed into a respective waveguide 225 a,225 b.

In step 603, the beam is shaped with the collimator 229 to form acollimated beam 205′. In an embodiment, in step 603 the beam is shapedwith the collimator 229 to form the collimated beam 205′ that isoriented in a third plane 234 (e.g. plane of FIGS. 2E, 2G). In someembodiments, in step 603 separate beams are transmitted from tips 217 ofthe waveguides 225a, 225 b and respective collimators 229a, 229 bcollimate the beams into respective collimated beams 205′ that areoriented in the third plane 234 (e.g. plane of FIG. 2G). In anembodiment, in step 603 the collimated beam 205′ is directed within thethird plane 234 in a direction toward one of the polygon scanners 244 a,244 b (FIG. 2E-2F) or toward both of the polygon scanners 244 a, 244 b(FIGS. 2G-2H).

In step 605, a direction of the collimated beam 205′ generated in step603 is adjusted in the first plane 235 with the first polygon scanner244 a from the first angle to the second angle in the first plane 235.In an embodiment, in step 605 the beam 233′ is scanned over the lowerscan region 264 based on the rotation of the first polygon scanner 244 aaround the rotation axis 243. In an embodiment, in step 605 the scanner241 directs the beam 233 onto the facets 245 of the first polygonscanner 244 a for a period of time that is sufficient to scan the beam233′ with the first polygon scanner 244 a from the first angle to thesecond angle. In an example embodiment, for the system 301′, step 605involves scanning the beam 233′ from the first angle to the second angleover the first plane 235 that is oriented toward the surface 349.

In step 607, one or more return beams 291 are received at the waveguidetip 217 of the system 200″ based on the adjusting of the direction ofthe beam 233′ in the first plane 235 in step 605. In an embodiment, instep 607 the return beams 291 are processed by the system 200″ in orderto determine a range to the target over the lower scan region 264. In anexample embodiment, in step 607 the return beams 291 are reflected fromthe surface 349 (or a target on the surface 349) based on the adjustingof the direction of the scanned beam 233′ in the first plane 235.

In step 609, the direction of the beam 205′ is adjusted in the thirdplane 234 (plane of FIG. 2E) from the first polygon scanner 244 a to thesecond polygon scanner 244 b. In an embodiment, in step 609 thedirection of the beam 205′ is adjusted with the scanner 241 at acontinuous scan speed that is sufficiently slow that steps 605 and 607are performed as the beam 205′ is on the facets 245 of the first polygonscanner 244 a. In an embodiment, in step 609 the direction of the beam205′ is adjusted with the scanner 241 at a non-zero scan speed betweenthe scanners 244 a, 244 b and is held fixed on each of the scanners 244a, 244 b until steps 605, 607 (for scanner 244 a) or steps 611, 613 (forscanner 244 b) is performed. In some embodiments, where separate beams205′ are transmitted onto the separate polygons scanners 244 a, 244 b(e.g. FIGS. 2G-2H), step 609 is omitted.

In step 611, a direction of the collimated beam 205′ generated in step603 is adjusted in the second plane 237 with the second polygon scanner244 a from the first angle to the second angle in the second plane 237.In an embodiment, in step 611 the beam 233′ is scanned over the upperscan region 262 based on the rotation of the second polygon scanner 244b around the rotation axis 243. In an embodiment, in step 611 thescanner 241 directs the beam 233 onto the facets 245 of the secondpolygon scanner 244 b for a period of time that is sufficient to scanthe beam 233′ with the second polygon scanner 244 b from the first angleto the second angle. In an example embodiment, for the system 301′, step611 involves scanning the beam 233′ from the first angle to the secondangle over the second plane 237 that is oriented toward the target 343on the surface 349 (e.g. at a maximum range from about 150 m to about400 m). In an embodiment, the direction of the adjusting of the beam233′ in the second plane 237 in step 611 is opposite to the direction ofthe adjusting of the beam 233′ in the first plane 235 in step 605.

In step 613, one or more return beams 291 are received at the waveguidetip 217 of the system 200″ based on the adjusting of the direction ofthe beam 233′ in the second plane 237 in step 611. In an embodiment, instep 613 the return beams 291 are processed by the system 200″ in orderto determine a range to the target over the upper scan region 262. In anexample embodiment, in step 613 the return beams 291 are reflected fromthe target 343 based on the adjusting of the direction of the scannedbeam 233′ in the second plane 237.

In step 615, it is determined whether more swipes of the beam 233′ inthe first plane 235 and/or second plane 237 are to be performed. In anembodiment, step 615 involves comparing a number of swipes of the beam233′ in the first plane 235 and/or second plane 237 with a predeterminednumber of swipes of the beam 233′ in the first plane and/or second plane237 (e.g. stored in the memory 704). If additional swipes of the beam233′ are to be performed, the method 600 moves back to step 605. Ifadditional swipes of the beam 233′ are not to be performed, the method600 ends. In one embodiment, the polygon scanners 244 a, 244 bcontinuously rotate at fixed speeds during the steps of the method 600.In one embodiment, when the method 600 ends the processing system 250transmits a signal to the polygon scanners 244 a, 244 b to stop therotation of the scanners.

In an embodiment, the method 600 further includes determining a range tothe target in the first plane 235 and/or second plane 237 based on thereturn beam data received in steps 607 and 611. Additionally, in oneembodiment, the method 600 includes adjusting one or more systems of thevehicle 310 based on the range to the target in the first and secondplane 235, 237. In an example embodiment, the method 600 includesadjusting one or more of the steering system and/or braking system ofthe vehicle 310 based on the target range data that is determined fromthe return beam data in steps 607 and 611.

7. Computational Hardware Overview

FIG. 7 is a block diagram that illustrates a computer system 700.Computer system 700 includes a communication mechanism such as a bus 710for passing information between other internal and external componentsof the computer system 700. Information is represented as physicalsignals of a measurable phenomenon, typically electric voltages, butincluding, in other embodiments, such phenomena as magnetic,electromagnetic, pressure, chemical, molecular atomic and quantuminteractions. For example, north and south magnetic fields, or a zeroand non-zero electric voltage, represent two states (0, 1) of a binarydigit (bit). Other phenomena can represent digits of a higher base. Asuperposition of multiple simultaneous quantum states before measurementrepresents a quantum bit (qubit). A sequence of one or more digitsconstitutes digital data that is used to represent a number or code fora character. In some embodiments, information called analog data isrepresented by a near continuum of measurable values within a particularrange. Computer system 700, or a portion thereof, constitutes a meansfor performing one or more steps of one or more methods describedherein.

A sequence of binary digits constitutes digital data that is used torepresent a number or code for a character. A bus 710 includes manyparallel conductors of information so that information is transferredquickly among devices coupled to the bus 710. One or more processors 702for processing information are coupled with the bus 710. A processor 702performs a set of operations on information. The set of operationsinclude bringing information in from the bus 710 and placing informationon the bus 710. The set of operations also typically include comparingtwo or more units of information, shifting positions of units ofinformation, and combining two or more units of information, such as byaddition or multiplication. A sequence of operations to be executed bythe processor 702 constitutes computer instructions.

Computer system 700 also includes a memory 704 coupled to bus 710. Thememory 704, such as a random access memory (RAM) or other dynamicstorage device, stores information including computer instructions.Dynamic memory allows information stored therein to be changed by thecomputer system 700. RAM allows a unit of information stored at alocation called a memory address to be stored and retrievedindependently of information at neighboring addresses. The memory 704 isalso used by the processor 702 to store temporary values duringexecution of computer instructions. The computer system 700 alsoincludes a read only memory (ROM) 706 or other static storage devicecoupled to the bus 710 for storing static information, includinginstructions, that is not changed by the computer system 700. Alsocoupled to bus 710 is a non-volatile (persistent) storage device 708,such as a magnetic disk or optical disk, for storing information,including instructions, that persists even when the computer system 700is turned off or otherwise loses power.

Information, including instructions, is provided to the bus 710 for useby the processor from an external input device 712, such as a keyboardcontaining alphanumeric keys operated by a human user, or a sensor. Asensor detects conditions in its vicinity and transforms thosedetections into signals compatible with the signals used to representinformation in computer system 700. Other external devices coupled tobus 710, used primarily for interacting with humans, include a displaydevice 714, such as a cathode ray tube (CRT) or a liquid crystal display(LCD), for presenting images, and a pointing device 716, such as a mouseor a trackball or cursor direction keys, for controlling a position of asmall cursor image presented on the display 714 and issuing commandsassociated with graphical elements presented on the display 714.

In the illustrated embodiment, special purpose hardware, such as anapplication specific integrated circuit (IC) 720, is coupled to bus 710.The special purpose hardware is configured to perform operations notperformed by processor 702 quickly enough for special purposes. Examplesof application specific ICs include graphics accelerator cards forgenerating images for display 714, cryptographic boards for encryptingand decrypting messages sent over a network, speech recognition, andinterfaces to special external devices, such as robotic arms and medicalscanning equipment that repeatedly perform some complex sequence ofoperations that are more efficiently implemented in hardware.

Computer system 700 also includes one or more instances of acommunications interface 770 coupled to bus 710. Communication interface770 provides a two-way communication coupling to a variety of externaldevices that operate with their own processors, such as printers,scanners and external disks. In general the coupling is with a networklink 778 that is connected to a local network 780 to which a variety ofexternal devices with their own processors are connected. For example,communication interface 770 may be a parallel port or a serial port or auniversal serial bus (USB) port on a personal computer. In someembodiments, communications interface 770 is an integrated servicesdigital network (ISDN) card or a digital subscriber line (DSL) card or atelephone modem that provides an information communication connection toa corresponding type of telephone line. In some embodiments, acommunication interface 770 is a cable modem that converts signals onbus 710 into signals for a communication connection over a coaxial cableor into optical signals for a communication connection over a fiberoptic cable. As another example, communications interface 770 may be alocal area network (LAN) card to provide a data communication connectionto a compatible LAN, such as Ethernet. Wireless links may also beimplemented. Carrier waves, such as acoustic waves and electromagneticwaves, including radio, optical and infrared waves travel through spacewithout wires or cables. Signals include man-made variations inamplitude, frequency, phase, polarization or other physical propertiesof carrier waves. For wireless links, the communications interface 770sends and receives electrical, acoustic or electromagnetic signals,including infrared and optical signals, that carry information streams,such as digital data.

The term computer-readable medium is used herein to refer to any mediumthat participates in providing information to processor 702, includinginstructions for execution. Such a medium may take many forms,including, but not limited to, non-volatile media, volatile media andtransmission media. Non-volatile media include, for example, optical ormagnetic disks, such as storage device 708. Volatile media include, forexample, dynamic memory 704. Transmission media include, for example,coaxial cables, copper wire, fiber optic cables, and waves that travelthrough space without wires or cables, such as acoustic waves andelectromagnetic waves, including radio, optical and infrared waves. Theterm computer-readable storage medium is used herein to refer to anymedium that participates in providing information to processor 702,except for transmission media.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, a hard disk, a magnetic tape, or any othermagnetic medium, a compact disk ROM (CD-ROM), a digital video disk (DVD)or any other optical medium, punch cards, paper tape, or any otherphysical medium with patterns of holes, a RAM, a programmable ROM(PROM), an erasable PROM (EPROM), a FLASH-EPROM, or any other memorychip or cartridge, a carrier wave, or any other medium from which acomputer can read. The term non-transitory computer-readable storagemedium is used herein to refer to any medium that participates inproviding information to processor 702, except for carrier waves andother signals.

Logic encoded in one or more tangible media includes one or both ofprocessor instructions on a computer-readable storage media and specialpurpose hardware, such as ASIC 720.

Network link 778 typically provides information communication throughone or more networks to other devices that use or process theinformation. For example, network link 778 may provide a connectionthrough local network 780 to a host computer 782 or to equipment 784operated by an Internet Service Provider (ISP). ISP equipment 784 inturn provides data communication services through the public, world-widepacket-switching communication network of networks now commonly referredto as the Internet 790. A computer called a server 792 connected to theInternet provides a service in response to information received over theInternet. For example, server 792 provides information representingvideo data for presentation at display 714.

The computer system 700 can implement various techniques describedherein in response to processor 702 executing one or more sequences ofone or more instructions contained in memory 704. Such instructions,also called software and program code, may be read into memory 704 fromanother computer-readable medium such as storage device 708. Executionof the sequences of instructions contained in memory 704 causesprocessor 702 to perform the method steps described herein. Inalternative embodiments, hardware, such as application specificintegrated circuit 720, may be used in place of or in combination withsoftware to implement the invention. Thus, embodiments of the inventionare not limited to any specific combination of hardware and software.

The signals transmitted over network link 778 and other networks throughcommunications interface 770, carry information to and from computersystem 700. Computer system 700 can send and receive information,including program code, through the networks 780, 790 among others,through network link 778 and communications interface 770. In an exampleusing the Internet 790, a server 792 transmits program code for aparticular application, requested by a message sent from computer 700,through Internet 790, ISP equipment 784, local network 780 andcommunications interface 770. The received code may be executed byprocessor 702 as it is received, or may be stored in storage device 708or other non-volatile storage for later execution, or both. In thismanner, computer system 700 may obtain application program code in theform of a signal on a carrier wave.

Various forms of computer readable media may be involved in carrying oneor more sequence of instructions or data or both to processor 702 forexecution. For example, instructions and data may initially be carriedon a magnetic disk of a remote computer such as host 782. The remotecomputer loads the instructions and data into its dynamic memory andsends the instructions and data over a telephone line using a modem. Amodem local to the computer system 700 receives the instructions anddata on a telephone line and uses an infra-red transmitter to convertthe instructions and data to a signal on an infra-red a carrier waveserving as the network link 778. An infrared detector serving ascommunications interface 770 receives the instructions and data carriedin the infrared signal and places information representing theinstructions and data onto bus 710. Bus 710 carries the information tomemory 704 from which processor 702 retrieves and executes theinstructions using some of the data sent with the instructions. Theinstructions and data received in memory 704 may optionally be stored onstorage device 708, either before or after execution by the processor702.

FIG. 8 illustrates a chip set 800 upon which an embodiment of theinvention may be implemented. Chip set 800 is programmed to perform oneor more steps of a method described herein and includes, for instance,the processor and memory components described with respect to FIG. 7incorporated in one or more physical packages (e.g., chips). By way ofexample, a physical package includes an arrangement of one or morematerials, components, and/or wires on a structural assembly (e.g., abaseboard) to provide one or more characteristics such as physicalstrength, conservation of size, and/or limitation of electricalinteraction. It is contemplated that in certain embodiments the chip setcan be implemented in a single chip. Chip set 800, or a portion thereof,constitutes a means for performing one or more steps of a methoddescribed herein.

In one embodiment, the chip set 800 includes a communication mechanismsuch as a bus 801 for passing information among the components of thechip set 800. A processor 803 has connectivity to the bus 801 to executeinstructions and process information stored in, for example, a memory805. The processor 803 may include one or more processing cores witheach core configured to perform independently. A multi-core processorenables multiprocessing within a single physical package. Examples of amulti-core processor include two, four, eight, or greater numbers ofprocessing cores. Alternatively or in addition, the processor 803 mayinclude one or more microprocessors configured in tandem via the bus 801to enable independent execution of instructions, pipelining, andmultithreading. The processor 803 may also be accompanied with one ormore specialized components to perform certain processing functions andtasks such as one or more digital signal processors (DSP) 807, or one ormore application-specific integrated circuits (ASIC) 809. A DSP 807typically is configured to process real-world signals (e.g., sound) inreal time independently of the processor 803. Similarly, an ASIC 809 canbe configured to performed specialized functions not easily performed bya general purposed processor. Other specialized components to aid inperforming the inventive functions described herein include one or morefield programmable gate arrays (FPGA) (not shown), one or morecontrollers (not shown), or one or more other special-purpose computerchips.

The processor 803 and accompanying components have connectivity to thememory 805 via the bus 801. The memory 805 includes both dynamic memory(e.g., RAM, magnetic disk, writable optical disk, etc.) and staticmemory (e.g., ROM, CD-ROM, etc.) for storing executable instructionsthat when executed perform one or more steps of a method describedherein. The memory 805 also stores the data associated with or generatedby the execution of one or more steps of the methods described herein.

Having now described some illustrative implementations, it is apparentthat the foregoing is illustrative and not limiting, having beenpresented by way of example. In particular, although many of theexamples presented herein involve specific combinations of method actsor system elements, those acts and those elements can be combined inother ways to accomplish the same objectives. Acts, elements andfeatures discussed in connection with one implementation are notintended to be excluded from a similar role in other implementations orimplementations.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including” “comprising” “having” “containing” “involving”“characterized by” “characterized in that” and variations thereofherein, is meant to encompass the items listed thereafter, equivalentsthereof, and additional items, as well as alternate implementationsconsisting of the items listed thereafter exclusively. In oneimplementation, the systems and methods described herein consist of one,each combination of more than one, or all of the described elements,acts, or components.

Any references to implementations or elements or acts of the systems andmethods herein referred to in the singular can also embraceimplementations including a plurality of these elements, and anyreferences in plural to any implementation or element or act herein canalso embrace implementations including only a single element. Referencesin the singular or plural form are not intended to limit the presentlydisclosed systems or methods, their components, acts, or elements tosingle or plural configurations. References to any act or element beingbased on any information, act or element can include implementationswhere the act or element is based at least in part on any information,act, or element.

Any implementation disclosed herein can be combined with any otherimplementation or embodiment, and references to “an implementation,”“some implementations,” “one implementation” or the like are notnecessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described in connectionwith the implementation can be included in at least one implementationor embodiment. Such terms as used herein are not necessarily allreferring to the same implementation. Any implementation can be combinedwith any other implementation, inclusively or exclusively, in any mannerconsistent with the aspects and implementations disclosed herein.

Where technical features in the drawings, detailed description or anyclaim are followed by reference signs, the reference signs have beenincluded to increase the intelligibility of the drawings, detaileddescription, and claims. Accordingly, neither the reference signs northeir absence have any limiting effect on the scope of any claimelements.

Systems and methods described herein may be embodied in other specificforms without departing from the characteristics thereof. Furtherrelative parallel, perpendicular, vertical or other positioning ororientation descriptions include variations within +/−10% or +/−10degrees of pure vertical, parallel or perpendicular positioning.References to “approximately,” “about” “substantially” or other terms ofdegree include variations of +/−10% from the given measurement, unit, orrange unless explicitly indicated otherwise. Coupled elements can beelectrically, mechanically, or physically coupled with one anotherdirectly or with intervening elements. Scope of the systems and methodsdescribed herein is thus indicated by the appended claims, rather thanthe foregoing description, and changes that come within the meaning andrange of equivalency of the claims are embraced therein.

The term “coupled” and variations thereof includes the joining of twomembers directly or indirectly to one another. Such joining may bestationary (e.g., permanent or fixed) or moveable (e.g., removable orreleasable). Such joining may be achieved with the two members coupleddirectly with or to each other, with the two members coupled with eachother using a separate intervening member and any additionalintermediate members coupled with one another, or with the two memberscoupled with each other using an intervening member that is integrallyformed as a single unitary body with one of the two members. If“coupled” or variations thereof are modified by an additional term(e.g., directly coupled), the generic definition of “coupled” providedabove is modified by the plain language meaning of the additional term(e.g., “directly coupled” means the joining of two members without anyseparate intervening member), resulting in a narrower definition thanthe generic definition of “coupled” provided above. Such coupling may bemechanical, electrical, or fluidic.

References to “or” can be construed as inclusive so that any termsdescribed using “or” can indicate any of a single, more than one, andall of the described terms. A reference to “at least one of” ‘A’ and ‘B’can include only ‘A’, only ‘B’, as well as both ‘A’ and ‘B’. Suchreferences used in conjunction with “comprising” or other openterminology can include additional items.

Modifications of described elements and acts such as variations insizes, dimensions, structures, shapes and proportions of the variouselements, values of parameters, mounting arrangements, use of materials,colors, orientations can occur without materially departing from theteachings and advantages of the subject matter disclosed herein. Forexample, elements shown as integrally formed can be constructed ofmultiple parts or elements, the position of elements can be reversed orotherwise varied, and the nature or number of discrete elements orpositions can be altered or varied. Other substitutions, modifications,changes and omissions can also be made in the design, operatingconditions and arrangement of the disclosed elements and operationswithout departing from the scope of the present disclosure.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below”) are merely used to describe the orientation of variouselements in the FIGURES. It should be noted that the orientation ofvarious elements may differ according to other exemplary embodiments,and that such variations are intended to be encompassed by the presentdisclosure.

What is claimed is:
 1. An apparatus, comprising: a motor; a firstscanner coupled to the motor, the motor configured to rotate the firstscanner at a first angular velocity about a rotation axis to deflect afirst beam incident in a third plane on the first scanner into a firstplane different from the third plane; and a second scanner coupled tothe motor, the motor configured to rotate the second scanner at a secondangular velocity different from the first angular velocity about therotation axis to deflect a second beam incident in the third plane onthe second scanner into a second plane different from the third plane.2. The apparatus of claim 1, wherein the first scanner is a firstpolygon scanner and the second scanner is a second polygon scanner. 3.The apparatus of claim 1, wherein: the first scanner is configured todeflect the first beam from a first angle in the first plane to a secondangle in the first plane less than or equal to sixty degrees from thefirst angle in the first plane; and the second scanner is configured todeflect the second beam from a first angle in the second plane to asecond angle in the second plane less than or equal to sixty degreesfrom the first angle in the second plane.
 4. The apparatus of claim 1,wherein the first scanner is configured to rotate in a differentdirection than the second scanner.
 5. The apparatus of claim 1, whereinthe first scanner is configured to scan a first region and the secondscanner is configured to scan a second region, the first region belowthe second region relative to the third plane.
 6. The apparatus of claim1, further comprising a third scanner configured to adjust a directionof the first beam from the first scanner to the second scanner.
 7. Theapparatus of claim 1, wherein the motor comprises a drive shaft and aplanetary bearing mounted to the first scanner through a recess of thefirst scanner that receives the drive shaft and the planetary bearing,and wherein the apparatus further comprises: a plurality of planetarytransmission gears; a driver sun gear; and a ring gear, the plurality ofplanetary transmission gears and the driver sun gear positioned withinthe ring gear, the second scanner mounted to the first scanner by theplurality of planetary transmission gears and the driver sun gear, atleast one parameter of at least one of the plurality of transmissiongears, the driver sun gear, or the ring selected to configure a ratio ofa magnitude of a rotation speed of the first scanner to a magnitude of arotation speed of the second scanner to be greater than
 1. 8. Theapparatus of claim 1, wherein the first scanner is configured to scanthe first beam over a first time period and the second scanner isconfigured to scan the second beam over a second time period after thefirst time period.
 9. The apparatus of claim 1, wherein a rotation speedof the first angular velocity is in a range from about 1000 revolutionsper minute (rpm) to about 5000 rpm and a rotation speed of the secondangular velocity is in a range from about 200 rpm to about 1000 rpm. 10.The apparatus of claim 1, wherein the motor comprises a first motorconfigured to rotate the first scanner and a second motor configured torotate the second scanner.
 11. The apparatus of claim 1, wherein: theapparatus is mounted to an autonomous vehicle, the apparatus furthercomprising a waveguide configured to receive at least one return beamcorresponding to at least one of the first beam or the second beam andprovide a signal corresponding to the at least one return beam to avehicle controller; and the vehicle controller is configured to controlat least one of a direction or a speed of the autonomous vehicleresponsive to the signal corresponding to the at least one return beam.12. A system, comprising: a laser source; at least one waveguideconfigured to receive a first beam from the laser source and emit thefirst beam at a tip of the at least one waveguide; at least onecollimator configured to collimate the first beam from each respectiveat least one waveguide into a third plane; a motor; a first scannercoupled to the motor, the motor configured to rotate the first scannerto deflect a second beam corresponding to the first beam into a firstplane different from the third plane; and a second scanner coupled tothe motor, the motor configured to rotate the second scanner to deflecta third beam corresponding to the first beam into a second planedifferent from the third plane.
 13. The system of claim 12, wherein: theat least one waveguide includes a first waveguide and a secondwaveguide; and the at least one collimator includes a first collimatorconfigured to collimate the first beam from the first waveguide to beincident on the first scanner and a second collimator configured tocollimate the first beam from the second waveguide to be incident on thesecond scanner.
 14. The system of claim 12, wherein: the first scanneris configured to deflect the second beam from a first angle in the firstplane to a second angle in the first plane less than or equal to sixtydegrees from the first angle in the first plane; and the second scanneris configured to deflect the third beam from a first angle in the secondplane to a second angle in the second plane less than or equal to sixtydegrees from the first angle in the second plane.
 15. The system ofclaim 12, wherein the first scanner is configured to rotate in adifferent direction than the second scanner.
 16. The system of claim 12,further comprising a third scanner configured to adjust a direction ofthe first beam from the first scanner to the second scanner.
 17. Thesystem of claim 12, wherein the motor comprises a drive shaft and aplanetary bearing mounted to the first scanner through a recess of thefirst scanner that receives the drive shaft and the planetary bearing,and wherein the apparatus further comprises: a plurality of planetarytransmission gears; a driver sun gear; and a ring gear, the plurality ofplanetary transmission gears and the driver sun gear positioned withinthe ring gear, the second scanner mounted to the first scanner by theplurality of planetary transmission gears and the driver sun gear, atleast one parameter of at least one of the plurality of transmissiongears, the driver sun gear, or the ring selected to configure a ratio ofa magnitude of a rotation speed of the first scanner to a magnitude of arotation speed of the second scanner to be greater than
 1. 18. Thesystem of claim 12, wherein the first scanner is configured to scan thesecond beam over a first time period and the second scanner isconfigured to scan the third beam in the second plane over a second timeperiod after the first time period.
 19. The system of claim 12, whereina rotation speed of the first scanner is in a range from about 1000revolutions per minute (rpm) to about 5000 rpm and a rotation speed ofthe second scanner is in a range from about 200 rpm to about 1000 rpm.20. The system of claim 12, wherein: the at least one waveguide isconfigured to receive at least one return beam corresponding to at leastone of the second beam or the third beam and provide a signalcorresponding to the at least one return beam to a vehicle controller;and the vehicle controller controls at least one of a direction or aspeed of the vehicle responsive to the signal corresponding to the atleast one return beam.